Charlotte - very pretty and feminine, though Charlie is a very popular nn, what about Clara or Chloe?
Coral - I think this is a beautiful name! If it doesn't feel substantial enough for you what about Coralie or Coraline?
Brielle - it is a bit on the trendy side, but not too bad imo. Briella?
Breanna - what about Bryony or Briony? Or even Brigitta? too weird? Breanna just feels a tad dated to me, since those I know are all in their 20's. It's a nice enough name, but between the last two I'd prefer Brielle.
Avani - never heard of this one before, it's interesting, a nice sound and a nice nn. I don't really love or hate it.
Charlotte (he really likes this but is it too popular? I don't like the nicknames Char or Lottie, and definitely not Charlie)-it's a classic. It is quite popular right now, but I love it nevertheless. Love the nn Lottie!
Coral (I love the colour and we both like the sea reference, but is it ok for a name?) - I would prefer Cora over Coral. My 2nd choice would be Coralie. Coral is ok too, but it makes me think of coral reefs and scuba diving.
Brielle (does this sound too.. pop singer-ish?)-It does have a pop-singerish vibe, but the "elle" grounds it a bit. I definitely prefer it over Brianna, but it's not a favorite of mine in comparison to your other choices.
Breanna (we both like the nickname Bre, but wondering if the ending "anna" is overused... not liking Breanne as much)-reminds me too much of Brianna. I just can't seem to get on board with Bri names.
Avani (Ay-vah-nee, I like the nickname Ava but is it too plain?)-I think it's nice, but I also think people won't always pronounce it the way you want them to. I can see some people saying Uh-va-nee, others Eh-va-nee and the rest will say the way you want them to. As someone with a name like that, I will tell you - it does get annoying. If you really like it, it's a good name for a mn spot. Charlotte Avani, Coral Avani, Brielle Avani, Breanna Avani. They all sound nice with Avani.
Out of your choices I really like Brielle and Breanna. I do agree with Katylou and Mischa. If you like and want a French name usuable in both languages you might like a real French name. And Coralie is quite charming and popular in France (at least when I was living there about 2 years ago).
Thought of a few more:
Vivienne- means "life," a very springy meaning. Also, it's French.
Esmeralda- since your little one is due in May and you mentioned you like jewel names...it means "emerald' which is May's birthstone
Calla- means "beautiful," and makes me think of Calla Lillies so gives off a springtime vibe
Cordelia- means "daughter of the sea," and you mentioned you like Coral for the sea reference.
Thank you for your comment :) I do like Coralie but we're both thinking she'd end up getting Cora as her nickname - it's ok but neither of us likes it due to a popular restaurant in the area called "Cora's"