musical beds

okay so we have 2 bedrooms upstairs and 3 down stairs with a rumpus room. We also have 4 boys who live with us full time and a girl who only stays once a fortnight. I know it is early days but I am trying to figure out how to shuffle rooms to fit a new baby as well as keep the other kids happy.
DS15,DS13,DS12,DD12,DS8 (all 2 are mine and 3 are his from previous marraiges).

The 3 oldest boys are currantly down stairs and the youngest shares with the daughter.

I idea at the moment is to move the DS8 down stairs to the rumpus room and bubs with us untill it is sleeping through the night. Bubs would then have the upstairs room next to us but DD12 would also have to sleep there on the 1 night she is here.

Is it possible to get a bunk set that fits a cot underneath? Any suggestions would be greatfully accepted.

Downstairs rooms are only big enough for 1 kid.