[DF is fiance, not father ]
The arrangement now is: DD1 (3 and a half) sleeps in the bottom bunk of bunk beds. The top bunk is not in use and has the ladder removed for now but when DD2 is older they will both be in the bunks. DD2 (14 months) is in a cot bed. DSS (3) stays one night a week and stays either in DD1's bottom bunk or on a trundle bed in the same room. They all like it this way.
We are renting and have a long term (5 years at a time) contract with our landlord. We don't want to move but want another DC. We have a large box room that's big enough to fit a single bed/bunk beds and a chest of drawers. Not spacious but spacious enough. I said to DF that our future baby would sleep with us for the first few months like all our children and then would move into a cot bed in the box room, later upgrading to a bunk bed which DSS could then have if he wanted not to be with his sisters.
DF is adamant we can't have another baby in there as although now it's used as a storage room it will be DSS' room when he wants it. I say having a bedroom would be nice for him but he stays one day a week and that plan is indefinite for at least a decade when DSS can legally decide himself who he wants to live with.
DF says we should move to a four bedroom house (which we can't afford realistically - I love this house, location, price, the layout, everything) if we wanted another DC. He thinks IABU for thinking this is a good idea.
Is three in a room one night a week too much? Would it be silly to put a cot in a smaller room and just upgrade to bunk beds for all the children as needed?
Sorry this is long.