3 year old DS shares a room with 9 year old DS. They have shared since YDS was 6 months old. ODS wanted his baby brother to share his room at the time and they both still love it.

They have both asked for their new baby brother to join them and we plan to move him in there when he's sleeping through the night.

I shared a room with my sister, who is 8 years younger than me, when I was a kid from the time she was born. But it was really the only choice in our 3BR house with 4 kids (2 boy, 2 girl). For most of that time, it was annoying only in the way that sharing space with a sibling is annoying, and my parents did add 2 more bedrooms into the basement by the time I was in HS and really wanted my own space that did not have a Barbie dream house in it.
If you do not have any other choice in your current house, I would hope that your kids would understand.

Anyone have 3 kids of same sex sharing a bedroom? Our DC 3 is much younger (5 and 7 years younger than older two sibs). Worried the big kids will be annoyed if a 2 year old joins them. Anyone put a much younger sibling in bedroom with older gradeschool one?