Adele is a beautiful name. Not too common but not too 'out there'. I LOVE it!
Mina actually is a given name in Sanskrit.
I think that Mina & Adele are both perfectly fine as full names.
I think Mina is wonderful on its own, it does not seem to be nicknamey at all.
The same goes for Adele.
Mina is fine on it's own, but I like Jessamina given the tie with her aunt. It sounds like you're open to middle names, so that makes the family connection with the first name even more important in my mind.
Let's see, what would work with Jessamina nn Mina . . .
oo I love Jessamina Helene. Something about the vowel sounds make it very smoooooth I feel like! :)