Hmmm It sounds a bit cramped? How long do they stay with their father? Does he have an extra room he uses for something else?
You could suggest letting the two younger girls have the bunkbeds and then putting the older son in a different room.
I could see this becoming more of an issue as the two older siblings age, since your daughter is so much younger than they are. So best to address it with the father now and find a better arrangement.




