DEMON SLAYER SWAP AU: Analysis and timeline (as accurate as it can be)

As it's title suggest, I'm gonna write how the timeline would have been if it was the swap au. I try to swap everything or as many things as possible but there are a few things I can't change or can't accurately swap. Because of trying to be as accurate as possible, it will result in the original timeline being broken at some places, or some characters can't even be swapped without changing the important things or there will be characters who wouldn't be even born or alive this way.