What time of year are you going to be there? And for how long? We like Dolly's Splash Country water park -- have gone there a few times for DGS's birthday. You could fill up a day at Dollywood and different members of the family would find at least one or two things to enjoy, probably several. That does sound like a lot of money, tho, plus food. We haven't gone for a few years now that DGS is not as interested in trains.
There are tons of the usual tourist-y things to do (mini-golf, go-karts, simulators, Titanic Museum, etc.). MagiQuest would be fun for the kids (maybe even the 19 yo) for a couple of hours. There's a good aquarium in Gatlinburg. Tons of shopping in both towns (actually, it's kind of three towns run together now -- Sevierville, PF, and G'burg). River raft rides?
If you like to visit National Parks, the Great Smokey NP is next door, but it might not offer you much since you're from NH -- unless you just like the Parks and want to check off one of the most visited ones on your list.
If you make a day trip to Asheville for the Biltmore Estate, be sure to leave PF really early in the morning; it takes at least 4-5 hours (or more) to enjoy what the Estate has to offer. (It's also very expensive).