Almost 3 years between DD1 and DD3. They currently share a room, but only started when DD2 was 2 1/2, prior to that she was co-sleeping with us. So I can't really comment on putting a baby in with a sibling.

At the moment the sleeping arrangements mostly work. There is the odd fight about lights out and what music to put on (they have sleepy music). Most of all they seem to like each others company. DD1 will complain of being lonely if DD2 sneaks back into our room.

All you can do is try it and see how they go.