We are also a family of 5 but our kids are a little older(18, 13, and 10). When we went last time they gave us a car to ourselves and we had the two youngest in the front, the 18 yo in the middle and me and the husband in the back. it worked out great! We were in a car with bench seating the there was definitely extra room for another body, even in the booth with my husband and I.
Additional note, you will definitely be inside a car. on our last trip we learned that with any adr you are guaranteed a car unless you say other wise.
Have fun! our 10 and 13 yo absolutely love this place!