We have four(!) boys (11,7,5,3) sharing a room. We stagger their bedtimes, so if one kid is super tired, he has a chance to fall asleep before his next playmate arrives. Sometimes, it actually works.
For us, we make the expectation clear, that they are to stay in their beds, and we don't let them do books or toys in bed.
To the OP, don't stress too much about it. For some reason, our boys get along better when they're supposed to be going to sleep than at pretty much any other time. They could be fighting like cats and dogs during the day, but the moment they get in their beds, they're best friends. Go figure. (sleep being a common enemy, perhaps?)