We currently have a 3 bedroom house. DD & DS currently have their own rooms & this new little bub will change that & two of the kids will need to share....but which two?

DS is 4.5yrs & DD is 2.5yrs and they are best of friends. DS is very keen to have this bub in his room though (he has the smallest room) & DD is still a bit too young to get the whole thing. So we're kind of stumped & don't know what to do. It's not something that has to be done before the baby is born as the baby will be in our room for a while but we'd like to have some direction as to what we will be doing. I feel the options that would make the most sense are to have DS & DD share DD's room, they both sleep through the night (DS starts school next year) OR do we have DD & this new bub share a room & leave DS where he is.

For those of you who have had to make this decision, what have you found has worked best? I'm sure whatever we do it will be fine but I really have nothing to base my decision on. So any help would be very much appreciated!