There are some cabins that only sleep 3. The reservation system won’t let you book more people in a cabin then fit ( 4 people in a cabin that only sleeps 3)
The cabins have a queen bed (it doesn’t separate to two beds)
The 3 person cabin will have a couch that folds down to a twin bed.
The 4 person cabin will have the same but a twin bunk that folds down from the ceiling
The 5 person cabin adds a additional twin Murphy Bed) that folds down from the wall.