So, we had 3 kid bedrooms and 4 kids....
For a long time, we had the older two (both girls) have their own rooms, and the younger two (both boys) share a room. Until the oldest girl was leaving for college / mission / etc. Then the Older two girls shared a room, and the two younger boys got their own rooms. Between college, summer internships, missions, etc, the older two girls really only had a few months of BOTH being in the room at the same time in like 5 to 8 years.

So, the younger two had to share until they were 8 or 9, and the older two had to share ("share" in quotes since they were seldom there at the same time) from 18 to 26.