Yes, if you request a burger at dinner, they will usually be happy to fix one for you--it's not on the regular dinner menu though, so you will need to ask.
And as for seating...
There are 'cars' that are actually set up as table seating, as oppossed to having the booths in front and back seats, that can accomidate groups of more than four (I think perhaps up to 8 people?). There are also a limited number of picnic tables and round 'umbrella' tables in the rear of the restaurant, for groups that prefer to be seated together as oppossed to in the car seat booths.