I believe it's more possible the protagonist be related to Crescent, because him/her is the only one Crescent seems to care (after all, she sent Nim to attack Melia and the rest of the gang, except the protagonist). I also believe Melia to be Vitus and Nymiera's , since she looks a lot like Maria(nette), but it's unlikely to be Anathea's, since she was already dead, and Isiah's description of "Anathea" sounds much more like Nymiera's description, and it talks about 4 children of the couple( Melia, Erin, Allen and Alice)