Okay people, this may be a lit bittle clarifying. Actually, a lot. Ninian goes to the place where her father left her and Nils. After getting there again with Eliwood and his party, after the battle, Lyn says that Ninian is looking at an eerie picture of a dragon and a human. It's heavily implied that the dragon is Aenir (Ninian's mother) and the human is Nergal. And a bit later, when Eliwood's party leaves, Nergal gets to the same place, saying that he has left something valuable there. Ok, just watch the beginning and the end and it'll be implied, if not clear, that Nergal actually IS the father of the dragon siblings.
