Hi Jenn,
We have eight children in two not very large bedrooms, and personal space is a definite challenge. The largest bedroom has five girls and one three year old boy, and the tiny bedroom houses our thirteen year old son and eighteen month old boy. Don’t ask me where the new baby will sleep in January…. because I don’t know and am losing sleep over it!!
I would suggest a small special chest for special things (small so that the special things are really special). High shelves in a closet also work well for the things that really must be kept away. I would encourage you to be careful with this, however. It’s good for them to learn to share. Ours are happier for it.
Also, nothing replaces teaching good old respect for privacy. This is difficult at the beginning with small children, but pays off in the long run. They can learn more quickly than I thought that everything is not theirs 🙂
If you are sure you want them to share the room, I would encourage you to move them in well in advance of the babies’ arrival. Too many changes at once are never fun. As they get older, you can re-evaluate and put all the girls together if that seems best (in my opinion, likely it will by then). But I definitely understand you wanting the babies having their own room right now.
Blessings to you as you prepare for your growing family.