It literally makes no logical sense whatsoever to say that gays should be adopt their own biological children. It is accepted by logicians that a child necessarily has the same parents in every possible world:
It's a game with magic, but that doesn't make the game illogical. Magic is not a violation of the laws of logic. It would literally be a violation of the laws of logic for, say, Camilla to have been born to different parents. You don't see violations of the laws of logic in Fire Emblem Fates, do you? Do you see square circles and other kinds of logical contradictions in FE14? No.