That's a perennial problem with both alternate universe and alternate timeline stories. Realistically, something as complex as DNA combinations, not to mention relationships and timing of 'encounters', would be so subject to the butterfly effect that nobody conceived after the diverging event would be the same person as anyone in the original timeline.
But the whole point of stories like this is to explore and have fun with different versions of well-established characters, so it's something that just has to be let slide for the sake of the story.