We have [name]Katherine[/name] ([name]Kate[/name]) and [name]Alexander[/name] ([name]Alex[/name]) already and are expecting a 3rd. It will be a surprise so we are looking to pick one name for each sex. Does [name]Greta[/name] go with our names already do you think? [name]How[/name] about [name]Lauren[/name]??
Boys I am lost so far. My luck that is what he will be! 
Thanks
You have two classic, formal names that are easily translated and have great nicknames. So I vote for [name]Margaret[/name] nn [name]Greta[/name] (although I don’t really care for [name]Greta[/name], having known one) or [name]Laura[/name], as opposed to [name]Lauren[/name]. [name]Lauren[/name] is so 70’s.
Boys are easy. [name]Alexander[/name] is either Scottish or Greek, so that’s where I would go:
[name]Philip[/name], [name]George[/name], [name]Michael[/name], [name]Peter[/name], [name]Paul[/name], [name]Constantine[/name], [name]Theodore[/name], [name]Andrew[/name], [name]Stephen[/name], [name]Christopher[/name], [name]Christian[/name], etc.
[name]James[/name], [name]Andrew[/name], [name]Francis[/name], [name]Charles[/name], [name]William[/name], [name]Edward[/name], [name]Edmund[/name], [name]George[/name], [name]Thomas[/name], [name]Frederick[/name], [name]Angus[/name], [name]Archibald[/name], [name]Crispin[/name], [name]Malcolm[/name], [name]Donal[/name], [name]Duncan[/name], [name]Robert[/name], [name]Roderick[/name], [name]John[/name]/[name]Iain[/name].
I think [name]Margaret[/name] nn [name]Greta[/name] would be great with your kids.
I also don’t like [name]Lauren[/name]. It’s sort of a mom name at this point, which is the fate of formerly trendy names of that sort. What about [name]Laura[/name] instead? [name]Katherine[/name], [name]Alexander[/name], and [name]Laura[/name] would be much better.
What about [name]Theodore[/name] nn [name]Theo[/name]? I always though [name]Alexander[/name]/[name]Alex[/name] and [name]Theodore[/name]/[name]Theo[/name] would be a good sibset.
I can see why you are leaning towards [name]Greta[/name] with [name]Kate[/name] and [name]Alex[/name] but while I absolutely love [name]Katherine[/name] and [name]Alexander[/name] I don’t love either [name]Margaret[/name] or [name]Gretchen[/name].
I do however think that [name]Eliza[/name] and [name]Imogen[/name] would make a really good fit, followed by a soft willowy middle name eg [name]Eliza[/name] [name]Willow[/name] and [name]Imogen[/name] [name]Laurel[/name].
For a brother I like [name]Lucas[/name] and depending on your style a middle like
[name]Lucas[/name] [name]Maxwell[/name]
[name]Lucas[/name] [name]Holden[/name]
[name]Lucas[/name] [name]Hudson[/name]
[name]Lucas[/name] [name]Neville[/name]
[name]Lucas[/name] [name]Gordon[/name]
or
[name]Miles[/name] [name]Connor[/name]
[name]Miles[/name] [name]Ezra[/name]
[name]Miles[/name] [name]Andrew[/name]
[name]Miles[/name] [name]William[/name]
or
[name]Lachlan[/name] [name]Connor[/name]
[name]Lachlan[/name] [name]Richard[/name]
[name]Lachlan[/name] [name]Grant[/name]
rollo
I’m with you [name]Rollo[/name], not a fan of [name]Margaret[/name], but like how [name]Greta[/name] sounds with my kiddos names. Such dilemmas. [name]Lucas[/name] is cute! I’ll have to run that by hubby!
[name]Theodore[/name] is one we have been throwing around. I like it and I don’t, ya know! I’m too picky maybe! 
I just want something that flows with my other kids names, there are many names I like, but they just don’t “go”! I appreciate your suggestions…and would love any more than anyone has!!! That is how I found [name]Greta[/name], a friend was just throwing out names!
I think I may have found a solution for you, it has the soft, sweet sound of [name]Katherine[/name] and blends beautifully with [name]Alexander[/name] and the name is [name]Gretel[/name]. If you named her [name]Gretel[/name] she could very easily have the nn of [name]Greta[/name], voila problem solved!
[name]Do[/name] you like [name]Gretel[/name]?
Good luck with [name]Lucas[/name] let us know if DH likes it.
best wishes
rollo
Ya know, it is funny you say that because I was tossing [name]Gretel[/name] around! 
[name]Greta[/name] is one of my favorite names. I like [name]Gretel[/name] too, but I would just stick with [name]Greta[/name].
[name]Lauren[/name]/[name]Laura[/name] all seem dated and bland to me.
I think any classic name would really go with your kids’ names: [name]Margaret[/name] (nn [name]Greta[/name]), [name]Elizabeth[/name], (nn [name]Liza[/name]). What about [name]Flora[/name]? It’s like [name]Laura[/name] but has a little more personality, and isn’t as common. As people above have mentioned, [name]Lauren[/name] is a bit dated.
For boys, I love [name]Edward[/name] (nn [name]Eddie[/name]), [name]Frederick[/name] (nn [name]Fred[/name]), and [name]Gregory[/name] (nn [name]Greg[/name]) with your kids’ names.
I honestly feel that [name]Gretel[/name] is the answer. Firstly, it is such a sweet, gentle name like [name]Katherine[/name]. It is unusual but not weird, or in the trying too hard basket, and is the perfect place to come from if she becomes a [name]Greta[/name]. I think that all your children’s names have an international flavour as well as an Anglo/Aussie/American feel too, and that they all work together just perfectly. I hope that [name]Gretel[/name] ticks all the boxes for you; it is imo the perfect fit.
best wishes,
rollo 
Now only to find a boys name. Why oh why did I want a surprise?! LOL
[name]Lauren[/name] is an ok name- not spectacular, not bad, just eh ok. I coached quite a few kids named [name]Lauren[/name] ranging from elementary school through high school aged.
A girl that is my age (27-28) that I went to college with is named [name]Greta[/name]-just [name]Greta[/name]. My neice is also [name]Greta[/name]. I love the name and had it on my list until my sister used it for her daughter! I think it can stand on it’s own just fine, but I can see why you may want a formal name for your third child.
As for boys maybe
[name]Leo[/name]
[name]Andrew[/name] nn [name]Drew[/name]
[name]Dominick[/name] nn [name]Dom[/name] or [name]Nick[/name]
[name]Jerimiah[/name]
I’m not the best with boys- sorry!
Isn’t [name]Nicholas[/name] a handsome name? I met one yesterday and the name wowed me again. You can also go with the nn of [name]Cole[/name] if you choose not to go with nn of [name]Nick[/name].
Yes, I don’t have any problem with just [name]Greta[/name], but it seems brief and informal next to [name]Katherine[/name] and [name]Alexander[/name].
[name]William[/name]
[name]Thomas[/name]
[name]Henry[/name]
[name]Peter[/name]
[name]Timothy[/name]
[name]Benjamin[/name]
[name]Zachary[/name]
[name]Julian[/name]
[name]Oliver[/name]
[name]Nathaniel[/name]
[name]Gabriel[/name]
[name]Frederick[/name]
[name]George[/name]
[name]Christopher[/name]
[name]Isaac[/name]
[name]George[/name]
[name]Walter[/name]
[name]Arthur[/name]
[name]Charles[/name]
[name]Tobias[/name]
[name]Jonathan[/name]
[name]Anthony[/name]
[name]Abraham[/name]
[name]Nicholas[/name]
[name]Isaiah[/name]
[name]Elijah[/name]
[name]Ezekiel[/name]
[name]Sebastian[/name]
[name]Edward[/name]
[name]Francis[/name] ([name]Frank[/name] is cool)
[name]Lionel[/name]
[name]Louis[/name]
[name]Maxwell[/name]
[name]Patrick[/name]
[name]Phillip[/name]
[name]Victor[/name]
[name]Vincent[/name]
I love [name]Gretel[/name]!
I think [name]Gretel[/name] may be more diminutive than [name]Greta[/name]. [name]Both[/name] [name]Greta[/name] and [name]Gretel[/name] are nn for [name]Margarete[/name]. The way [name]Kate[/name] and [name]Katie[/name] are both nicknames for [name]Katherine[/name]. Like this:
[name]Margarete[/name]/[name]Margareta[/name]/[name]Margarethe[/name] ~ [name]Katherine[/name]
[name]Greta[/name] ~ [name]Kate[/name]
[name]Gretel[/name]/[name]Gretchen[/name] ~ [name]Katie[/name]
I think adding the -[name]CHEN[/name], -[name]EL[/name], -[name]GEN[/name] at the end of [name]German[/name] names connotes diminutive status like adding -IE does for English names. But, hey, I could be wrong. I am not [name]German[/name]. And it won’t be the first (or last) time that I’ve been wrong!
But [name]Gretchen[/name] and [name]Greta[/name] seem to have lost their purely nn status (at least in the US). I’ve heard them used as names in their own right as much as or more than as nn. [name]Gretel[/name] may be losing its diminutive status as well. I’m considering [name]Greta[/name] for my own daughter to be born in a few months, but I don’t think I’d consider [name]Gretel[/name] in the same way that I could name a child [name]Kate[/name] but not [name]Katie[/name]. That’s just me.
To the point: I love your son and daughter’s names. If you want to match their formal names as much as possible, than I think [name]Margaret[/name] or it’s many variations [name]Marguerite[/name]/[name]Margarete[/name] etc are all good matches. [name]Gretel[/name]/[name]Greta[/name]/[name]Gretchen[/name] could always be nicknames. But, if I were in your shoes, I’d just pick my fave of the bunch since [name]Gretel[/name]/[name]Greta[/name]/[name]Gretchen[/name] aren’t necessarily considered only nn anymore.
They are all lovely!
Sorry for any repeats!
For girls maybe
[name]Alexander[/name], [name]Katherine[/name] and:
[name]Elizabeth[/name] nn [name]Ellie[/name], [name]Liz[/name], [name]Eliza[/name], [name]Beth[/name]
[name]Samantha[/name] nn [name]Sam[/name], [name]Sammy[/name], [name]Annie[/name] (bit of a stretch)
[name]Cassandra[/name] nn [name]Cass[/name], [name]Cassie[/name], [name]Sandra[/name], [name]Casey[/name], [name]Sandy[/name]
[name]Gabrielle[/name] nn [name]Gabby[/name], [name]Brielle[/name], [name]Elle[/name], [name]Ellie[/name], [name]Ella[/name]
[name]Charlotte[/name] nn [name]Lottie[/name], [name]Charlie[/name], [name]Lotta[/name]
[name]Madeline[/name] nn [name]Maddy[/name], [name]Della[/name]
[name]Rebecca[/name] nn [name]Becky[/name], [name]Becca[/name]
[name]Alice[/name] nn [name]Allie[/name], Lissy
[name]Delilah[/name] nn Dela, [name]Lila[/name], [name]Ellie[/name] (again)
[name]Sophia[/name] nn [name]Soph[/name], [name]Fia[/name], [name]Fee[/name], Flea
[name]Josephine[/name] nn [name]Jo[/name], [name]Josie[/name]
or for Boys:
[name]Benjamin[/name] nn [name]Ben[/name]
[name]Nicholas[/name] nn [name]Nick[/name], [name]Cole[/name]
[name]Nathaniel[/name] nn [name]Nathan[/name], [name]Nate[/name]
[name]William[/name] nn [name]Will[/name], [name]Liam[/name]
[name]Joseph[/name] nn [name]Joe[/name], [name]Joey[/name]
[name]Christopher[/name] nn [name]Chris[/name], [name]Christophe[/name]
[name]Zachary[/name] nn [name]Zach[/name]
[name]Sebastien[/name] nn [name]Seb[/name], [name]Bastien[/name]
[name]Gabriel[/name] nn [name]Gabe[/name]
[name]Elijah[/name] nn [name]Eli[/name]
Because of your previous choices of long, more formal full names with cute nick names, I also prefer [name]Margaret[/name] to [name]Greta[/name] or [name]Gretel[/name]. [name]Gretel[/name] mostly makes me think or [name]Hansel[/name] and [name]Gretel[/name] (no offense). I would go with a similar naming style of a formal long name with a nn for your third child.
I hope this helped!
Oh, I quite like [name]Kate[/name], [name]Alex[/name], and Annnie. Plus the best thing about [name]Annie[/name] is that so many names have “an” in them, you can find any longer version you like. [name]Diana[/name], [name]Frances[/name], [name]Susannah[/name], [name]Anastasia[/name], [name]Hannah[/name], [name]Antonia[/name], [name]Annabel[/name], [name]Bethany[/name], [name]Miranda[/name], [name]Angelica[/name], [name]Bianca[/name], [name]Cassandra[/name], [name]Johanna[/name], [name]Roxana[/name].