I've heard real good things about jackrabbit in haynesville.
^^this place^^
I've been to all the trails mentioned with my young kids and Jackrabbit easily takes the top spot on the podium.
Tsali is basically flat and boring for WNC standards. Yes, it is technically mountain biking, but it's far from exciting.
Fire Mountain is a very good time, but you do have to climb up to get down. The climb up Uktena is actually pretty average for the area (2 miles, 800 feet). Your family will love the flow of the descents and there is virtually no tech to hurt you.
Jackrabbit on the other hand is pretty much the perfect combination of mild, intermittent climbs, and really nice twisting flow. Whoever built this trail system (kudos to you!), did a proper job. Great tread, light tech, with lots of loop options. Plus the beach at Jackrabbit campground is sublime compared to the clay based yuck of Fontana Lake.
Choose Jackrabbit over all the others. You and the kids won't be disappointed.