We too are a party of 5. We just returned from POR and were impressed with the resort. Our DD is still only 2 so we were considered a party of 4 therefore we didn't request the trundle bed. We stayed in AB 14 and it was a great location but the resort was so pretty we wouldn't have minded a longer walk. Even though we didn't request it, a trundle bed was in the room. The trundle bed was small. Plenty big enough for our kids who are only 5, 4 & 2 but too small for an adult or large teen. We let our kids take turns sleeping on it each night. Whoever slept on it that night got to answer the wake up call from Mickey.
There is so much to do at POR that the kids will enjoy. The fishing hole, which we didn't get to do, looks like fun. They have the carriage rides there and the bus to DD disney. The arcade was pretty large and free entertainment Thursday-Saturday at the River roost. The kids also loved the pool and playground area.
As far as other places for a family of 5 to stay we will be looking into that too when DD turns 3. We have stayed at the Poly which sleeps 5 but is also so much more $ than POR. We are thinking of staying in a Wilderness cabin in the spring. They are reasonable with the AP rates. They can sleep 6. There is also the option of getting 2 connecting rooms but that depends on the ages of your kids and the size of your wallet.
I would suggest POR because it is so beautiful and is the best option for the price, IMO.
If you have any other questions about POR, I'd be glad to try and help.