My husband, my girl and myself have stayed in a room with 4 beds before, don't know if it's Deluxe房或plaza premier房. The room is spacious with large bathroom, especially we got 1 extra bed to put our shopping stuffs, very good!
We asked for 3 beds per room, but they give us a family room with 4 beds.
The 2nd time we went to Keio Plaza, they gave us 3 beds per room at the old wing, the room is a bit older, but still have enough space to move around with 3 beds.
I think we are lucky to stay in the 4 beds room last time.