Yvaine is probably a feminine variant of Yvain, who btw is a knight in the arthurian mythology. I would pronounce it "Eev-ehn" in French but english speakers would probably say "Eev-ayne", which sounds even better imo.
Incidentally this is the middle name I have for ds2 (the male version, Yvain) due in may.
I do like Serafina, it's original and really nice with lots of nickname options.
The french version of the name is Séraphine (it's a type of angel, which I'm sure you already know). But I like the Serafina spelling.
With a long name as first name I'd pick a short middle name such as Lea, Leigh, Belle, Briar, Blair, Claire, Dawn, Eve, Zoë...
Though I do like Yvaine a lot for a girl, too 😊