Find out about all the things there are to do in the places you are going, that includes the stuff you already mentioned, as well as touristy stuff, even amusement parks, or what ever attractions you can find.
Have a couple of family meetings about your trip (with that many kids you won't get this done in an hour). Present each leg of the trip to the kids and possible activities. Let them pick things they want to do. The family should agree that each one gets to do one thing they really want to do sometime on that trip, even the adults. Then mix in the things that more than a one wants to do. Then aside from the "must do" things, leave it loose, that is leave room to make last minute changes for things you find out about when you get there, that sort of thing.
We did things this way and had very memorable trips. And those family meetings built up excitement for the trip. Your kids will NOT sleep the night before you leave.
Gatlinburg. We're going there in Sept. Great Smokey Mountains NP could keep you plenty busy just by itself. We're spending 80% of our time there day hiking.
