We have six children, and are expecting our seventh, in a 3-bedroom home. Our children have always- and will always- have to share a bedroom with one another, and and as a result, we have had to deal with various sleep issues from time to time.
We have spent many evenings visiting in the living room outside of their open doors to monitor and correct their behavior instead of retiring to our bedroom. It has also been helpful to send them to bed a little earlier so that there is time for the "winding down" to take place. Currently, we send certain children to bed early while allowing the others to stay up and play quietly. (I don't think it's fair to make the 10yo go to bed at the same time as the 3yo anyway.)
If you choose to put your boys back together, remain patient and understand that you may have to deal with some problems- though it sounds to me that you have merely traded one set of problems for another by separating them in the first place. If you are willing to work with them, to teach them to stay in bed and go to sleep when they are in the same room together, I think it would be best. None of our children like to sleep alone. In fact, they all sleep together in a pile on the floor rather than in their own beds! (That's another tactic we use- we make them sleep in their beds as a punishment for excessive chatter and horseplay before bed! How weird is that???) I would never split them up into their own rooms now when they feel more comfortable and secure being together.
Just my 2 cents... Best of luck in whatever decision you make.
C., soon-to-be mommy of 7