I just finished watching Season 3 Episode 14, where an elderly man and woman had their respective spouses die in each Universe. Their elevated emotions created what was described as quantum entanglement (scientifically nonsense, of course, but that's not why we're here). This created a 'soft spot' and unexplained phenomena throughout the building. The way to stop this from tearing apart the Universe was to convince the elderly woman that her 'husband' was not really her husband, which she discovered after the other Universe's husband had told her that her children missed her, despite the fact that she never had children in her Universe.
How, then, does everyone currently have their own doubles? Are we to believe that every other person and couple had children the same between Universes?