My dyslexia disfigured your post. I had to read it several times before my brain unscrambled it. And hot.
Good to see that you didn't clench your jaw on this one. Like, I came into this thread expecting a Digimon joke, but somehow I still feel it was a worthwhile click. Banter aside though, I think it's sad that they broke up because if nothing else, they could have adopted a child or used the magic of science/douching to lessen the chances of giving birth to a zombie. This likely wouldn't have been an option for their 1st child, but if they wanted a 2nd/for others/etc. You can call it incest or whatever, but it's not like we live in a world of completely traditional families anyways, and it's not like they were fucking in the cradle.
I suppose you have the small hope it's just a half sibling over a whole sibling /shrug it's worth a shot, for what little it's worth!
Everyone should have a DNA chip in their hand that beeps when they encounter someone that's closely genetically related to them. Meet a new person and shake their hand. If it beeps then don't hump them.