We also have 3 bedrooms. We have the eldest 2 in one room, the middle 2 in another and the youngest is still in with us. Eventually he'll go in with the middle 2. That was something a friend said to me with ds5, "where are you planning to put this one?"
At one point we had 4 kids in a 2 bed. We had 2 sets of bunk beds. There was also a stage where we needed to separate them and so we had a sofa bed downstairs for a while.
We've never had too much of a problem with it, though we've swapped who shared with each other a couple of times depending on who was getting along at the time.