This is a different Owen pregnant. The one that usually wears the handkerchief around the neck.
Does this mean it will be just one baby then?
The handkerchief Owen will have one baby if I remember right. I don't remember if the other Owens have a child with nux.
Is it because he's not the "main" Owen, so he won't have multiple babies???
If you are referring to the fact asangards (or however it is spelled) have different manifestations of them selves from different worlds/timelines showing up in the world, then yes the handkerchief Owens' child could have different versions of itself just like Noi. But it is not certain yet since we have caught up with the raws.
He's pregnant AGAIN?!?! Doesn't that mean they're gonna have 4 more kids making it 8?!? That's a lot. To manage.