I'd approve only if
Callie and
Maddie were nicknames. Think about how the names will age. Just use them as nicknames. This reminds me of a sibset of
Kara and
Maddie (
Madelyn) that I know of.
Callie and
Maddie is very cute, though I'm not actually crazy about either in real life. I'd suggest Calandra and
Madeleine or
Maddalena as full names personally, though theire are many to choose from.