[name_m]Hi[/name_m] there.
[name_u]Luca[/name_u] is such a beautiful name, & I love [name_f]Celia[/name_f] for his little sister. It’s smart & pretty & not too popular but not too complicated.
Here are my thoughts on your mn ideas so far:
[name_f]Celia[/name_f] Moon-I think that [name_f]Moon[/name_f] is maybe not my style…even though the moon itself is lovely. I just don’t like the way that it looks as a name. But this does flow well & has special meaning, so it seems like a great pick.
[name_f]Celia[/name_f] Ruby-Pretty cute, but doesn’t seem as special as some of the others.
[name_f]Celia[/name_f] Journey-That feels meaningful, but I don’t like [name_u]Journey[/name_u] as a name much either. 
[name_f]Celia[/name_f] Pearl-Stunning! I love [name_f]Pearl[/name_f]. It’s so vintage & charming. A heavenly pearl sounds majestic.
[name_f]Celia[/name_f] Caroline-Perfectly nice, but doesn’t sparkle.
[name_f]Celia[/name_f] Claire-Same as above. [name_f]Claire[/name_f] is a bit over done in the mn spot.
[name_f]Celia[/name_f] Rain-That’s kind of neat. Makes [name_f]Celia[/name_f] feels a bit hippie-ish, & I mean that in a good way!
[name_f]Celia[/name_f] Iris-This seems like the natural choice. I don’t love [name_f]Iris[/name_f] myself or the flow that much, but it doesn’t sound bad.
[name_f]Celia[/name_f] Bloom-I like the idea of things blooming, but not [name_f]Bloom[/name_f] much for a name.
[name_f]Celia[/name_f] Skye-I love [name_u]Skye[/name_u] in general. Maybe not the alliteration, but I can’t decide!
A few more ideas:
[name_f]Celia[/name_f] [name_f]Adeline[/name_f]
[name_f]Celia[/name_f] [name_f]Daphne[/name_f]
[name_f]Celia[/name_f] [name_f]Fern[/name_f]
[name_f]Celia[/name_f] [name_u]Indigo[/name_u]
[name_f]Celia[/name_f] [name_u]Juniper[/name_u]
[name_f]Celia[/name_f] [name_u]June[/name_u]
[name_f]Celia[/name_f] [name_f]Marigold[/name_f]
[name_f]Hope[/name_f] this helps. 