M.R.
I have had to change my kids' routines a few times since they started sharing. They are 20 months apart and started sharing when the younger was a year old. Originally it was easier to put the little one down and bring the older one up when his brother was sleeping since he would whisper and try not to "wake up the baby." Once he realized how fun it was to jump in the crib and wake his brother up, we had to change things again. Sometimes we've put them down at the same time, but usually since my oldest no longer naps (he's 4 now) I put him down first, give him 20 to 30 minutes to fall asleep (he is usually out in about 15) and then bring his brother up. I would put the soundest sleeper to bed first and wait if you don't want them playing. If they play for a while and still fall asleep at a decent time though I would let them play. Mine tend to get too rowdy with jumping between the beds, stripping their beds, emptying dresser drawers (I think they share bad ideas when they are left to their own devices) and then it takes at least an hour or two longer to get them both to sleep. Not worth it to me. They also love sharing a room and I don't think they would want their own even if we had another one. =)