[name_m]Hi[/name_m] there.
[name_m]Elijah[/name_m] & [name_m]Sebastian[/name_m] are very handsome.
Here are my thoughts on your list:
[name_f]Celia[/name_f]-This is beautiful. It’s smart, elegant, & kind sounding. I think that it fits fairly well w/your boys’ names.
[name_f]Layla[/name_f]-This is okay. It has a nice sound, but it’s just sort of trendy.
[name_f]Cora[/name_f]-This is sweet. I also like [name_f]Coraline[/name_f] & [name_f]Cornelia[/name_f] nn [name_f]Cora[/name_f].
[name_f]Verity[/name_f]-This isn’t bad. It’s not my style, but kind of interesting.
[name_u]Arden[/name_u]-Meh, this is alright. I don’t think that it has a particularly feminine sound.
[name_u]Aspyn[/name_u]-This is not my favorite. It’s a bit trendy, & I don’t like the ‘ass’ part, LOL.
[name_f]Fern[/name_f]-Cute! Very different yet simple. It has great vintage charm.
[name_u]Haven[/name_u]-Meh, this isn’t my favorite either.
[name_f]Ivy[/name_f] -Kind of cute. I like the idea of it, but sometimes it just reminds me of ‘I.V.’ …like what you get at the hospital.
[name_f]Calla[/name_f]-This is kind of fun. I love Callalilie!
From your list, I like [name_f]Cora[/name_f] & [name_f]Fern[/name_f] for twins. They’re a little different style from [name_m]Elijah[/name_m] & [name_m]Sebastian[/name_m], but they certainly don’t clash. They fit really well w/each other. [name_f]Celia[/name_f] & [name_f]Fern[/name_f] are nice too.
Other ideas:
[name_f]Aurora[/name_f]
[name_f]Aurelia[/name_f]
[name_f]Ada[/name_f]
[name_f]Clara[/name_f]
[name_f]Delia[/name_f]
[name_f]Freya[/name_f]
[name_f]Flora[/name_f]
[name_f]Gemma[/name_f]
[name_f]Juliet[/name_f]
[name_u]Juniper[/name_u]
[name_f]Lorelei[/name_f]
[name_f]Mirabel[/name_f]
[name_f]Rosalie[/name_f]
[name_f]Tallula[/name_f]
[name_f]Thea[/name_f]
[name_u]Vivian[/name_u]
[name_f]Violet[/name_f]
[name_f]Hope[/name_f] this helps. 