I don’t think you can go wrong with any of these options! [name_m]Raphael[/name_m] is my least favorite middle only because I adore the other ones ([name_u]Gabriel[/name_u] is one of my favorite names, and I love both [name_m]Fabian[/name_m] and [name_u]Florian[/name_u]). I think the flow is fine.
However, since your husband is not sure on [name_m]Fabian[/name_m] and [name_u]Florian[/name_u], [name_u]Sasha[/name_u] [name_u]Gabriel[/name_u] is my favorite.
Thank you both!
I know what you mean… I think it’s a combination of the repetitive vowel sounds plus the final-syllable stress of [name_m]Raphael[/name_m] — it feels like there are maybe too many unstressed syllables between SASHa raphaEL. Maybe? I don’t know, but I feel this a little bit too, much as I love [name_m]Raphael[/name_m].
Sasha would be such a wonderful addition to your family 
Out of your names, I have to say I feel [name_u]Florian[/name_u] would be the most similar to your other children middles. Bold, a little bit quirky, with that lovely romantic feeling…
About [name_m]Raphael[/name_m], I do like this name. It’s such a pity than in spanish almost every [name_m]Rafael[/name_m] I’ve met goes by [name_u]Rafa[/name_u]. To me, [name_m]Raphael[/name_m] feels retro, like an '80s name. I quite like the contrast in the name [name_u]Sasha[/name_u] [name_m]Raphael[/name_m], because [name_u]Sasha[/name_u] is such a soft name while [name_m]Raphael[/name_m], at least how I pronounce it, has a strong R sound. I don’t think [name_u]Sasha[/name_u] [name_m]Raphael[/name_m] sounds too choopy, and I guess he wouldn’t go by [name_u]Sasha[/name_u] [name_m]Raphael[/name_m] in his daily.
If your husband isn’t sure about [name_u]Sasha[/name_u] [name_u]Florian[/name_u] or [name_m]Fabian[/name_m], [name_u]Sasha[/name_u] [name_m]Raphael[/name_m] is definitely a great option.
About [name_u]Sasha[/name_u] [name_u]Gabriel[/name_u] it’s also a lovely name, and in my opinion the flow in this name is slightly better than in [name_u]Sasha[/name_u] [name_m]Raphael[/name_m], but I think [name_u]Gabriel[/name_u] feels to plain next to your other kids middles.
Thanks for such detailed feedback @UnderTheRainbow!
That’s my major stumbling block with [name_u]Gabriel[/name_u] — it’s handsome and romantic and lovely, but it does feel a bit more “basic” than the others, and my son’s middle name ([name_u]Valentine[/name_u]) in particular. I agree that [name_u]Florian[/name_u] would be a perfect fit! I love your description of it 
I really love how [name_u]Sasha[/name_u] [name_m]Raphael[/name_m] looks. While it doesn’t sound bad when said aloud, I think that the other names flow better. As mentioned before, he most likely would go by just [name_u]Sasha[/name_u] on a daily basis rather than [name_u]Sasha[/name_u] [name_m]Raphael[/name_m]. [name_f]My[/name_f] favorite would be [name_u]Sasha[/name_u] [name_u]Florian[/name_u]. To me it sounds soft but strong at the same time.
I love [name_u]Sasha[/name_u] [name_m]Raphael[/name_m] for you. I agree that [name_u]Gabriel[/name_u] has a better flow but feels too basic.
Raphael perfectly balances the romanticism of [name_f]Juno[/name_f] and [name_u]Valentine[/name_u], the normal-sounding yet unexpected qualities of [name_f]Matilda[/name_f], [name_u]Kit[/name_u], and [name_f]Helena[/name_f], and the cosmopolitan flair of [name_f]Anouk[/name_f] (and [name_u]Sasha[/name_u], for that matter).
Anouk and [name_m]Raphael[/name_m] also look so good next to one another. Something about all the vowels. [name_f]Anouk[/name_f] and [name_u]Sasha[/name_u] are perfectly trans-continental without being basic or bothersome, a quality that [name_m]Raphael[/name_m] also highlights without adding a single note of obnoxiousness.
It is just perfect. Have another kid already!
[name_m]Can[/name_m] you talk to my husband? 
I’m too busy talking to mine about a number 4…
You haven’t even had 3 yet!! 