The cars each have 3 benches that hold 2 adults each. I think there are a few shorter cars (only 2 benches) to fit into the restaurant but in all the times I have eaten here (at least a dozen), we have been seated in a 3 seated car and they do fill the car. Since you are 3, they will allocate 2 benches to you so you will have a couple of strangers (aka hitchhikers) sitting in front of you or behind you.
Every time we have dined there as a party of 2, we have been seated in the back, behind the party of 4. Maybe coincidence, I don't know.