I'll try and be brief! We have 3 DC. DS1 (4) currently in a single room on his own. B/G DTs (21m) currently in a double room together. We are considering a DC4 in a year or 2]so.
DS1 keeps asking to sleep in with DTs, he loves sharing with them when we go away etc. DTs will be moving to beds in about 6m. I thought it may make sense to have all 3 DC in the one room when this happens - using 2 bunk beds, DTs on lower, DS on top of one. This way DS1 is happy and will be used to sharing a room when the time comes for DD to need her own room (rather than leaving him on his own and then forcing him to move rooms to share with DS2 later when he may have decided his own room is quite nice!). It also allows DD to continue sharing with her twin until she feels ready to move as I am keen not to separate them until they are ready, so potentially not until puberty.
it also frees up the single room to be a nursery in the meantime if we do go for DC4. DC4 can then move to the spare bunk space and if a boy will stay in their with his brothers and if a girl we will move one set of bunks to the single room (its a generous single room) and have the boys in one and the girls in the other when DD1 is ready to leave her twin.
The double room is 14ft by 15ft so there is plenty of space and the children have a playroom of the same size so they don't play in their bedrooms, only sleep.
I think this is the best option but my MIL thinks I'm mad and DH isn't convinced. Your opinions please!