We store (as most people do) the empty suitcases under the beds. Then they are out of the way. As long as you can stack them inside each other you should be able to fit the "footprint" of 4 large suitcases under the beds and not have them out to be tripped on. We use a couple of large ones for a place to put dirty clothes too.
You should be fine.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007