I see
Mia as a full name, since it's not used as a nickname in the circles I run in. And I know
Andie seems like it should be a obvious nickname for
Andrea, but I've known about a thousand
Andreas and not a single one used
Andie, so I'm more apt to use it as a nickname for something like
Andromeda or
Alexandrina.
Alexandrina &
Mia are a bit mismatched though, so maybe I'd go with
Mariamne "
Mia" &
Alexandrina "
Andie". MAriamne was the first thing that came to my mind, and I do like that name. Very fanciful.
Mariamne Lila &
Alexandrina Zoe