Dear Ms. Q,
This is going to be an answer in at least two parts, because first we have to consider the lives that are living in each universe and then we have to consider the souls that are lived in each universe.
On the second part dealing with the soul, that will require much thought and meditation, but I will answer. So give me a little time to at least prepare the first part and then the second will come after.
I do have to say this, there are people who do believe this concept and there are people who also think that it is only theory that cannot be proven and therefore is more in the area of Science Fiction.
But I have always said "What If...." because there always seems to be a tug at these "what if's" so it is a 'theory' that is worth an explanation.
So keeping that in mind I will post as soon as I can the concept of Parallel Universes.
Blessings Ms. Q.