Tricky. Many years ago when my kids were little we lived in a one bedroom flat. So we more or less all slept in the same room(the kids had cots to sleep in). When we moved to a three bedroom flat it was very difficult to get them to sleep in their own rooms. But with gentle perseverance and a lot of cuddles and pep talks it happened naturally. All I can say is be patient and try to consider your gals` feelings and more importantly her sons, good luck with it and best wishes, Dionysius.