[name_m]Hi[/name_m] there.
I love [name_m]Fynn[/name_m]!
Here are my thoughts on your list:
[name_f]Ella[/name_f]-This is lovely. Short, sweet, vintage, grows up well. I don’t know of any nns other than [name_f]Elle[/name_f] or [name_f]Ellie[/name_f]. I actually kind of find [name_f]Ella[/name_f] nick-namey on its own, although I like just [name_f]Ella[/name_f] w/just [name_m]Fynn[/name_m]. But just in case, [name_f]Ella[/name_f] can be a nn for [name_f]Eloisa[/name_f], [name_f]Estella[/name_f], [name_f]Eleanora[/name_f], Miriella?
[name_u]Bailey[/name_u] / [name_f]Bailee[/name_f]-Meh, I don’t know. This seems sort of trendy & lacking substance. Sort of super popular for dogs too. And it’s not very feminine.
[name_u]Reese[/name_u]-This would be nice as a brother for [name_m]Fynn[/name_m], but not a sister in my opinion. [name_m]Even[/name_m] though it’s probably more popular for girls, it’s traditionally a boy name.
[name_u]Josie[/name_u]-[name_m]Fynn[/name_m] & [name_u]Josie[/name_u] are adorable, but I really love [name_f]Josephine[/name_f]. [name_f]Josephina[/name_f] is also pretty. [name_u]Josie[/name_u] is just really nick-namey to me, but at least it’s a sweet name.
[name_f]Georgia[/name_f]-This is nice. Has a Southern [name_f]Belle[/name_f] feel, which is charming. I love the nns [name_u]Georgie[/name_u] & [name_f]Gigi[/name_f]. I even more like [name_f]Georgina[/name_f] & [name_f]Georgiana[/name_f]. They’re fancier, which may or may not be what you’re looking for.
[name_u]Blakely[/name_u]-This seems very trendy & made up.
[name_f]Keira[/name_f]-Oh, I don’t know. It sounds pretty, but this spelling bugs me. I feel like the pronunciation is confusing. Is it ‘Kee-air-uh’ or ‘[name_m]Keer[/name_m]-uh’? I think that if you’re looking for the former, you should spell it [name_f]Ciara[/name_f]. And the latter, [name_f]Kira[/name_f]. Does that make sense? I think that [name_f]Ciara[/name_f] looks & sounds beautiful. And Gaelic next to [name_m]Fynn[/name_m].
[name_f]Amelia[/name_f]-I love this! It’s my kitty’s name. Too bad that you can’t use it, but at least you get to know one. 
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Other ideas:
[name_f]Azalea[/name_f]
[name_f]Chloe[/name_f]
[name_f]Calla[/name_f]
[name_u]Eloise[/name_u]
[name_f]Eve[/name_f]/[name_f]Evie[/name_f]
[name_u]Eliya[/name_u]
[name_f]Gemma[/name_f]
[name_u]Indigo[/name_u]
[name_f]Ivy[/name_f]
[name_f]Juliet[/name_f]
[name_f]Lilie[/name_f]
[name_f]Lucy[/name_f]
[name_f]Maisy[/name_f]…but I think that it’s better as a nn. Maybe you’d like [name_f]Madeline[/name_f] nn [name_f]Maisy[/name_f]?
[name_f]Magnolia[/name_f]
[name_f]Nora[/name_f]
[name_f]Primrose[/name_f]/[name_f]Rosie[/name_f]/[name_f]Posy[/name_f]
[name_f]Rosalie[/name_f]
[name_u]Ruby[/name_u]
[name_f]Stella[/name_f]
[name_u]Skye[/name_u]-That’s so cool w/[name_m]Fynn[/name_m].
[name_f]Sadie[/name_f]
[name_f]Tallula[/name_f]
[name_f]Violet[/name_f]
[name_f]Zella[/name_f]
[name_f]Hope[/name_f] this helps. 