Hi K.,
We had three children in one room for a long time - 2 boys and 1 girl. They were 4, 2 and a baby. When the 4th child came along, we moved the girl to her own room and then all 3 boys shared a room. We never had a problem with naps or disturbances. They actually liked sharing a room. When our daughter had her own room, she felt lonely and one of her brothers would often end up sleeping in her room.
Out kids never really played in their rooms though until they got older (like around 10) so maybe that's why we didn't have a problem. We were homeschooling and so much of our reading and other activities took part in the other areas of our home.
All my kids sleep really well. I believe that if they don't get used to really quiet times to sleep they tend to acclimate to some noise and then are not light sleepers that awaken at every sound. We had our babies nap in the living room in a port-a-crib during the day sometimes too.
Also, now that my kids are older (12, 14, 16 and 18), they look fondly on their times sharing rooms. They have many stories of talking together at night and listening to books on tapes together.
Good luck,
C.