I think having maximum one Hebrew name - to tie in with the three boys with them and one non-Hebrew to tie in with Felix would be good. Or both not Hebrew (not for any deep reason, just to balance) - looks like that’s the direction you’re going anyway.
I would also make them have different starting letter to anyone in family, and a different ending to each other as twins (eg not Willa & Nina/ Nina & Thea etc - too matchy and cute for twins).
I like all the names but my faves are:
Willa & Rose
Sylvie & Margot
Willa & Margot
Sylvie & Thea