Cars will seat 6 adults; each car has 3 bench seats that comfortably seat 2 adults. If you have young enough children, you might be able to squeeze 3 people into one seat (one adult with two kids or 3 kids).
Almost all of the seating in the restaurant is in the cars. We've eaten here about a dozen times and always get a car, regardless of party size. The half cars and tables are probably used for people who request it (some people prefer to sit facing one another rather than everyone facing forward in the cars).
If you are a party of 3 or 4, you will more than likely be given the first two bench seats in a car. If you are a party of 2, you will more than likely be seated as "hitchhikers" meaning you will get the back bench seat behind a party of 4 strangers. They will fill the cars, regardless of party size.
Our last time there, we were a party of 11 and we were seated in 2 cars side by side. They are pretty accommodating here.