Those jeweled eyes are probably real. They are simply not his is my guess and he has the ability to partly use them.
The reason why she probably looks like a monster to him my guess is because she has dual divinities. So she probably looks quite scary to him.
As for why she fainted, she probably felt the pain of the original owner of the jeweled eyes
Edit: as for the corpse thing, my guess is that being from that clan, when she gave birth alone the MC shoukd have disapeared also cause no one knew her. But the 2nd divinity counter balanced it.