DD and I always ride at Old Town. There is also a multi-level track we've passed a few times but have yet to visit on International Drive. It looks neat - we just haven't made it there yet.
Fun Spot is the place with the multi-level tracks. My guys LOVED this place last summer...spent hours upon hours there riding the go-karts and they're still talking about it. They have 2-rider go-karts too so kids who are too small to drive can ride. Google "fun spot orlando" and you'll find their website. Have fun!
By the way, Old Town also has 2-person karts. Actually, any go-kart track I've ever been to with DD has had 2-person karts. I think that's fairly common.