Separate rooms. One in each of our bedrooms and one in a crib in the daycare playroom. I see benefits to both ways (it's a lot of work to get them to 5 separate rooms). I think they learn how to tune each other out in one room...I've seen that with them in separate rooms but I think they sleep better this way, especially when a new one is adjusting and doesn't sleep well. That bit of space and wall helps!

I have a video monitor that covers 4 rooms and a regular monitor in the 5th room.