My older two will be sharing a room once baby arrives. They get along great and sleep well so I'm not hugely concerned about that part of it. But, I don't know which room to combine them into. My DD absolutely LOVES her current room. She gets so excited to show it to new visitors, likes to play quietly there, etc. and it is larger than my DS's room. So at first I thought it would make more sense to move him, given that he doesn't show any preference for his bedroom at that age, and she likes hers so much. But, the floor plan makes her bigger room super awkward for a sharing layout. We could make it work but it would always look sort of haphazard.
DS's room has a really easy layout for sharing, but it's smaller so very little of their personal things would fit. Toys, all but a few books, and even some clothes would have to be kept elsewhere.