In my own fiction (not published yet - though I'm getting closer) I have come up with an explanation for the same people showing up in alternate and/or parallel universes.
To wit, there are two kinds of what I call extra-dimensional avatars: hereditary avatars; people that, through some manner have ended up as the same people because their parents, grandparents, etc somehow managed to come together and reproduce at the same time, resulting in the same people being born, with the same DNA and appearance; and incidental avatars, people that, while appearing to be the same people, have different parents, are a different age, perhaps by as little as hours, and are not quite the same height or proportion.
This makes as much sense to me as I can make, and when I finally get such a story published, you can rest assured I'll make the explanation make as much sense as I can.
To wit, there are two kinds of what I call extra-dimensional avatars: hereditary avatars; people that, through some manner have ended up as the same people because their parents, grandparents, etc somehow managed to come together and reproduce at the same time, resulting in the same people being born, with the same DNA and appearance; and incidental avatars, people that, while appearing to be the same people, have different parents, are a different age, perhaps by as little as hours, and are not quite the same height or proportion.
This makes as much sense to me as I can make, and when I finally get such a story published, you can rest assured I'll make the explanation make as much sense as I can.