Did you try
(SPOILER)casting cure on the memories of your family in the little bubbles and then using the magicite that appeared? I found that out entirely by accident (I actually meant to cure myself), but it makes the battle quite easier. If it was eluded to somewhere, I missed it (I've never waited for
(SPOILER)all the Carbuncles in Mag Mell to wake up so I don't know if any of them tell you about that and they are the only ones I can think of that would give you a hint, aside from Mio [which, if she did so, I did not decipher it]).