Hi Melissa, and welcome!
Like you, we're a family of 5 returing to WDW next summer.
I'm not sure where you are in the planning process, so allow me to list the on site resorts that will accomodate a family of 5-- I'm pretty sure they're in order of increasing price. Disney resorts come in 3 different classifications: Value, Moderate, and Deluxe
- Port Orleans Riverside (moderate) has some rooms with a Murphy Bed.
- Two (hopefully) connecting (not just "adjoining") rooms at any Value
- Family Suite at All Star Music (value.)
- Family Suite at Art of Animation (value)
- Cabin at Fort Wilderness
- Deluxe: most of the Deluxes (with the exception of Wilderness Lodge and Animal Kingdom Lodge) have a daybed that will accomodate a 5th person, and they're sized so an adult can sleep there comfortably. The cheapest is probably a Garden Wing room at the Contemporary, followed by the Beach Club, Yacht Club and Boardwalk Inn, followed by the Polynesian and then the Grand Floridian.
Take a look at the slide shows and fact sheets at
www.allears.net to get a better idea of what each resort offers.
Also, if you have some wiggle room, make sure to book your trip during "Value II Season"-- it will save you some money. The allear link above will let you know when it starts for each of the different resorts.
Regardless of which resort you choose, you'll have Disney's Magical Express (a free ride to and from the airport), access to all Disney transportation on site, and access to Disney's Extra Magic Hours, times when the parks are only open to the guests at Disney resorts. (Yes, it's about 3 trillion people. But there are another 16 trillion who stay off site who don't have that EMH access.)
That should get you started.
