I very much like the 4th / Father theory. It makes sense in a weird kinda way... wouldn't you be late to your village getting destroyed if your son was being born? That's the kind of thing you just don't pass up.

"Hey honey, if you don't mind, you give birth and I'll go kill the demon" probably just wouldn't go over too well. Then the man would have two demons to fight. Haha, he'd have to seal his wife into Kyuubi, and then Kyuubi into Naruto.

-xtortout