I am laughing because we have the same situation...twice.
Our boys, now 6 and 8 share a room...and 2 of our girls 5 and 17 months share rooms. Before we moved, we had 4 kids all in 1 room (ages: 5,3,1, and newborn). So I have plenty of experience about sharing rooms :)
I used to get upset and try to take stuff away to get them to calm down, then I tried to run them like crazy up and down the stairs (the boys), adjusted their bedtime (which we still send them to bed earlier to give them time to chat, play, horse around...whatever. But then it dawned on me that I just need to chill out. Seriously. How awesome is it that my boys are talking to each other and WANTING to play together for a while. Don't get me wrong, we will still go in and tell them that it's time to be quiet... then we hear them "whisper". What's happening with my little girls now, is that I hear my baby trying to talk to her sister (she's still in a crib), and some nights, my husband and I will just turn the TV off and listen to the little girls giggle and we will listen to what the boys are saying and playing. It's neat to listen to them and see what they're thinking.
My best advice would be: run them like crazy before bed, put them down an hour before, when you tuck them in tell them that it's time to go "night-night" then close the door. Unless someone is in danger, just let them be for a while and just be patient. Go in 1/2 hour later or so and remind them that it's time to calm down and go to sleep like big boys. Eventually 1 is going to fall asleep before the other one, then the other one will get bored and go to sleep too.
We also played the "elf game" the first one to sleep for the night gets a prize in the morning. Usually a small piece of candy like a tootsie roll or sucker :)
Good luck and just be patient :)