Hello, Gina!
Unfortunately, you cannot sleep five Guests in a room which accommodates four people. Occupancy laws come into play here, so the rollaway bed would not be an option for you. These are offered to Guests on a case-by-case basis, such as a teenage girl who will not share a bed with a younger sibling, etc, rather than stretching the room's capacity.
I suggest you take a look at this link to
Rooms for 5 Guests or More, so that you'll have a better understanding of your options. Here, you'll find suggestions on rooms which can accommodate your party size, including
The Cabins at Disney's Fort Wilderness Resort, which not only sleeps 6 Guests, but also offers a full kitchen, one separate bedroom with a double bed and bunk beds as well as a double sleeper sofa in the living area, all for $285 a night. This might be a great option for your family, too, if you need the extra space for sleeping AND you get the luxury of having a full kitchen right in your room, a great plus when traveling with kids, who always seems to need a snack or a drink...;-)
Hope this helps! Send more questions as you think of them; we love to help!