Our # 4 was born when the triplets were 20 months old and we live in a 3 bedroom as well. We kept the triplets together and put the baby in her own room. Their play room became a gated area in an area off the kitchen.
I considered moving the baby in with the 3, but the schedules were really just too different. As it was, they would wake her up and she was constantly thrown off on her sleep schedules. Even now she does not get nearly the sleep she needs.

When she was 14 months old and the triplets were almost 3, we moved the big kids out of their cribs and into beds. At that time, we split the kids up- boys room and girl's room. And I also moved a few toys into their rooms.
Good luck!

Tiffany
BBG @ 31.4 weeks
on 11/27/06
3.11
3.6
2.14



baby girl born on 7/24/08