DD2 is in with us at the moment, and we have her nursery set up in a different room, but the plan is at the moment seeing how she sleeps after 9-12 months and then they will most likely share a room, and we will use the other as a toy room for them, and I can reclaim the 'activity' room.

Anyway, my newborn is a very good sleeper, and my 3 year rarely wakes overnight anymore. The newborn is a light sleeper, but sleeps through most nights and has done for a month.

I think the only way you will know is to wait and see what type of baby you will have. DD1 cried when she woke as a newborn, DD2 only grunts, DD1 woke at the latest every 4 hours, DD2 wakes once overnight only most nights.... They are both different, but I am hoping that the 'good' sleeping trend continues and they can both go into the same room when DD2 moves out of our room.