what about dropping miriam all together? i know you said your mom would be upset but im sure she will get over it. Good luck!
I think that [name]Thea[/name] [name]Blythe[/name] is the answer.
Your mother loves you and she would only want you to do what is in your heart. I think you are probably a free spirit and the family tradition of following the tradition is in a way stifling you. (No offense to Mum).
If [name]Thea[/name] [name]Blythe[/name] does touch your heart then that is the name for your baby. I would gently explain to Mum that in this case you are veering away from tradition, that is not to say that [name]Miriam[/name] cannot be used with a beautiful daughter later, no promises to Mum though.
(If you are Catholic and a confirmation name is chosen down the track you may select [name]Miriam[/name] or [name]Mary[/name] then?)
I like [name]Thea[/name] on its own better anyway without the [name]Al[/name] or An.
Listen quietly to your heart and to that of your husband’s and stay strong in the choice you make.
God Bless and more hugs.
Gosh, this is tough! I can only imagine how you and hubs must feel!
My daughter has two middle names. I get a lot of positive reactions to her name but people do make cracks about how long it will take her to write it out in kindergarten or how it will never fit in the space given on a standardized test sheet. I think in the case that there isn’t enough room you just go with the “first” middle name. That said, it IS kind of a lot to have two middle names and a hyphenated last name.
On the idea of dropping [name]Miriam[/name], if it’s important to you to keep tradition, then keep it, but if it’s much more important to other family, I would consider dropping it. They’ll balk at first, but they’ll get over it.
If [name]Thea[/name] and [name]Blythe[/name] are the names that hold the most meaning for you then a combo of the two feels like a good choice. It’s probably hard for you to really love ANY name when you’ve been thinking and talking about it so much… it probably all feels like it’s been talked to death and you just want it to be over with. I like the suggestion to take the pressure off yourselves and “try out” your potential names over a few days and see which name “takes.”
Good luck again! [name]Don[/name]'t be too hard on yourself! 
I like [name]Althea[/name], as well!
I’m now considering the option of two middle names… one has to be [name]Miriam[/name], but I’m wondering if there’s a way you creative ladies can help put these names together? - I don’t like this option with your last name.
Also- any experience with two mn’s? Does it get annoying? We also have two last names… similar to [name]Jackson[/name]-[name]Ford[/name]
Here’s what’s left of our list:
[name]Thea[/name] - Very pretty.
[name]Althea[/name]/[name]Elthea[/name] (DH likes the full versions more than just [name]Thea[/name], I don’t, but would compromise) - I like [name]Althea[/name] better than [name]Elthea[/name]. [name]Thea[/name] is a nice nn for [name]Althea[/name]
[name]Lark[/name] - It is very short and blunt to me.
[name]Blythe[/name] - I love this, love it with [name]Miriam[/name] so much. But I love [name]Thea[/name], too.
[name]Vega[/name] - I think this bugs me because it makes me think of Las [name]Vegas[/name]. I don’t like Las [name]Vegas[/name] at all. It makes me feel claustrophobic. I think the lights bother me, and all the noise. But that’s just me.
[name]Ever[/name] - my son has an awful apt. manager with this name. I am biased.
[name]Jewel[/name] - this feels kind of hard to me. But the singer [name]Jewel[/name] is amazing! [name]Love[/name] her voice! I love [name]Gemma[/name] so much more. Makes me think of an old, overgrown garden. [name]Jewel[/name] makes me think of a huge jewel with sharp edges. [name]Gemma[/name] is very soft. [name]Gemma[/name] [name]Miriam[/name] is way too “m” heavy though. Let us know if you need any more help. We are here for you! I love [name]Ruby[/name].
I love this Lamps!
I really like [name]Althea[/name]. It even has the possibility, if she so chooses to us the nn [name]Allie[/name].
I think that [name]Althea[/name] [name]Miriam[/name] [name]Blythe[/name] sounds fine. If you really love [name]Blythe[/name] though, you might want to hold on to it for a future daughter.
Best wishes and do let us know what you decide. 
Like everyone else, I feel for you in this difficult situation. I just wanted to add that I love [name]Thea[/name] [name]Blythe[/name] (if you decide to let go of [name]Miriam[/name]). But I also like [name]Thea[/name] [name]Miriam[/name]. I have to say that I don’t care for [name]Althea[/name] as much. [name]Theadora[/name] could be a more formal name for nn [name]Thea[/name] too.
[name]Thea[/name] [name]Blythe[/name] [name]Jackson[/name]-[name]Ford[/name]
[name]Thea[/name] [name]Miriam[/name] [name]Jackson[/name]-[name]Ford[/name]
[name]Theadora[/name] [name]Miriam[/name] [name]Jackson[/name]-[name]Ford[/name]
[name]Theodora[/name] is a great idea. But it’s spelled [name]Theo[/name] at the beginning, not [name]Thea[/name]. I think you could still get [name]Thea[/name] out of it as a nn. I also really love the name [name]Anthea[/name], but I always forget how to pronounce it. [name]Anthea[/name] nn [name]Thea[/name] is adorable!
If you want to make [name]Thea[/name] sound more special, how about pronouncing it as [name]Tay[/name]-ah? I think that sounds so cool with [name]Miriam[/name] and a possible future [name]Blythe[/name]! Good luck, I just know you’ll find the perfect name in the end! 
I feel for you, really, I do… I just asked my mum about one of the names I really like, Emrik, and she hated it (which is strange, because my brother is named [name]Bendik[/name])… It feels terrible not to have everyone on your side, especially since it isn’t something that will ever go away. Your child is named for life, and will always be around…
It seems like you really love [name]Thea[/name], so I’m going to suggest some alternative routes that you may not have considered yet… Also, I feel compelled to mention that the repetitive -th sounds of [name]Thea[/name] [name]Blythe[/name] makes it a bit awkward… I think if you separate the -th sounds with [name]Miriam[/name] it will sound better, choosing [name]Althea[/name] [name]Miriam[/name] [name]Blythe[/name] over [name]Althea[/name] [name]Blythe[/name] [name]Miriam[/name] if you decide to go with two middles…
Also, have you considered [name]Thea[/name] a nickname for [name]Blythe[/name]? It’s a stretch, but it’s not too far off the mark, and if you love both [name]Blythe[/name] and [name]Thea[/name], it’s a good way to get both, without having to resort to a second middle to fit [name]Miriam[/name] in… [name]Blythe[/name] [name]Miriam[/name] (nn [name]Thea[/name]) sounds good to me ^^
As for the case of two middles, I personally intend to use that myself, but it’s a very individual thing… You and your SO have to sit down and discuss if you really want that, because it might not be your style, and then you should avoid it! I wish you the best of luck on deciding, and I hope you find a name you can all be happy with, but remember that when it all comes down to it, it’s you and your man who has to love your daughters name, not necessarily your mum…
Finally, some more ways to get [name]Thea[/name], perhaps:
[name]Ianthe[/name]
[name]Thelma[/name]
[name]Thalia[/name]
[name]Alethea[/name] (I actually find this prettier than [name]Althea[/name]… More complete in a way, and sounds better with [name]Miriam[/name])
[name]Agatha[/name] (this may be a stretch, but if you’re consistent in calling her [name]Thea[/name] from the start, nobody will mind after a while…)
dearest - I even thought of [name]Thea[/name] as a nn for [name]Blythe[/name] since it ends in -the. I wonder how much of a stretch it really would be? I’m glad I’m not the only one who thought of it though.
I think you will come up with a name you will be happy with, and you have already received some great advice. I just wanted to add that I agree that 2 middle names might be a bit much with the hyphenated last name. Also, I think [name]Miriam[/name] is a lovely middle name, and it has been the one constant throughout your naming process. I think you should keep it. Middle names rarely get used, and they are a nice spot for honoring family or a family tradition. Since you have a family tradition that you have intended to honor for a while now, I would not be swayed from that. If you end up using the name you really want to use as the 1st name in the middle name slot, you may end up being disappointed because it will always be shunted to 2nd place.
As far as your 1st name choice goes, you have a beautiful baby whom you have already gotten to know whom you are now trying to name. I imagine this is a bit different from choosing the name before your child’s birth. But just because a name like “[name]Thea[/name]” doesn’t fit your daughter just right now does not mean it won’t come to suit her later. “[name]Thea[/name]” is a name that can work for her throughout her life, though I imagine few babies at 4 months would immediately stand out as a “[name]Thea[/name]”. It’s just that [name]Thea[/name] is not a baby name. (But I think it is a nice little girl name, teenager name, and grown up name.) While “[name]Lark[/name]” and “[name]Jewel[/name]” are also nice, they do not strike me as having as much maturity and working as well for your daughter as she grows. But I agree absolutely with the other people who said they would make darling pet names or terms of endearment.
It sounds like both you & your husband like [name]Thea[/name], though you have thought so much about it, it’s hard to get the right distance on it. But one of the things you said is that you really appreciate the meaning of “[name]Thea[/name]”. Since [name]Thea[/name] is your husband’s 1st choice, I imagine he’d be okay with sticking to that name without lengthening it in order to preserve the meaning that you so much appreciate. [name]Alethea[/name] is also beautiful, but it doesn’t have the same meaning & history as [name]Thea[/name].
If you do end up lengthening [name]Thea[/name], I also agree the person who wrote that [name]Alethea[/name] would make a better choice than [name]Althea[/name] or [name]Anthea[/name]. The latter two names are much less familiar to me & strike my ear a little oddly. [name]Alethea[/name], though, is one of my favorites.
[name]Thea[/name] [name]Miriam[/name]. If this ends up being your daughter’s name, I think she will treasure it.
I don’t know if this has already been settled on, but I wanted to throw out the suggestion of [name]Theadora[/name] as a “full” first name. I think it’s a beautiful, classic name, and would easily lend itself to the nickname of [name]Thea[/name]. I also think the nickname [name]Dory[/name] is SO cute for a baby.
I’m sorry - I looked up [name]Theadora[/name], and it is a variation on [name]Theodora[/name]. [name]Theadora[/name] nn [name]Thea[/name] would be lovely!
[name]Don[/name]'t have a ton of time to reply, but wanted to thank you all incredibly for the feedback. It has been taken to heart and we are trying to take the pressure off (again) and come to a loving decision for our DD.
I’m warming to [name]Thea[/name] again. I [name]LOVE[/name] [name]Blythe[/name]. It is [name]Lark[/name] without the problems. I think I would be sad to give up the family tradition of [name]Miriam[/name]… that said, my mom and I might have to have a heart-to-heart about it because I promised her I would continue it and I don’t want to break my promise b/c DH and I can’t agree.
Because [name]Thea[/name] is DH’s top choice and [name]Blythe[/name] I think is mine… [name]Thea[/name] [name]Blythe[/name] [name]Jackson[/name]-[name]Ford[/name], while redundant on the ‘th’ as someone said, isn’t horrible is we are both getting to give her top choices, no?
Still considering [name]Thea[/name] [name]Miriam[/name] [name]Blythe[/name] [name]Jackson[/name]-[name]Ford[/name]. Huge mouthful, great story. Everybody happy? maybe? Use [name]Lark[/name] and [name]Jewel[/name] as pet names.
The thought of [name]Thea[/name] as a nn for [name]Blythe[/name] is certaily worth considering… kind of a strech, but not a huge one…
We did consider [name]Theodora[/name], I think it is a great name, DH was not sold, plus it loses the history of [name]Thea[/name] that I was originally attracted to.
Point being, THANK YOU again. I had no idea what I was stumbling upon with the board; you ladies give GREAT advice. [name]Will[/name] keep you updated. Keep opinions coming!
Best.
One other thought I just thought I’d toss out …
The name [name]Thea[/name] has a few different possible pronunciations – pronounced THEE-a or [name]THAY[/name]-a or [name]TAY[/name]-a or perhaps even TEE-a. Perhaps you will find that one of the other pronunciations has more bounce or appeal for you.
Best of luck.
Any chance you’ll be having more kids? If so, you could always save [name]Blythe[/name] for a possible future daughter.
Keep us posted! I’m hoping you’ll keep [name]Miriam[/name] though. [name]Thea[/name] [name]Miriam[/name] still gets my vote…