While i would love to have my boys in separate rooms again, they've had to share a room for almost 9 months now. They were ages 13 months and 3 years when they started. We moved out of state and were renting while our house sold, but it still hasn't. The whole time, we thought we'd be there for 1-2 months, so we told the older one that he'd have his own room again soon. Once he actually asked if, when we finally did buy a new house, could he still share a room with baby brother? he really enjoys it. I think they love each other even more than before, if that's possible.
The baby was a light sleeper despite all my efforts to train him to sleep through noise, and I anticipated lots of problems. But he sleeps through a lot now. In fact, once he FELL asleep and took a nap while workers were sawing a hole in the basement wall (for a window) just outside his window.
One problem was getting them both to bed at the same time. The baby liked to cry himself to sleep still, or sing, or jabber. And then the older one would yell at him to go to sleep. Obviously, that didn't work. Finally, we put the baby down and did something special, like have dessert or color or read books with the older one for about 15-20 minutes, by which time the baby was asleep. Then we'd tuck in the older one.
They've been sick this winter, and have awaken each other a few times. usually the older one sleeps through the baby crying, but if the 4 year old cries for some reason, they're both up. That's tough. Just recruit your husband to get one of them calmed down. I really wish DH were here on those nights!