My son is 6'4 and 300 lbs and has no trouble fitting in any of the four seats (yeah, ok, middle rear seat isn't too comfy) and regular size humans can sit behind or in front of him. I think he actually fits better than I do, in fact.
The one caveat is that he has to jack the seat all the way down, while I (at 5'6") have to jack it all the way up. A bit of a pain swapping drivers. If you're in a similar two wildly different size driver situation, it might be worth looking into an electric seat option. But with the seat in the right position, it's very comfortable for either of us.