We have a similar problem and our son (now 50 and our daughter now (10mth) share a room. It is sometimes a problem when she wants a nap and he is on the computer or something, but they love sharing a room together. Ari loves waking up and seeing her big brother and vice versa. As she is a restless sleeper I often worry that she is distrubing his sleep but he doesn't seem to wake when she cries.

With the cot rails up DS has no chance of being able to get in with her or anything like that. I think they sleep better together than she did by herself as she can hear his breathing and knows someone is with her. HTH