Sounds like fun
but i'd avoid making it too complicated, mixed ability teams and all laps count seems better to me and won't need a rocket surgeon to work it out at the end!
Also just keep it open within the time of 2.4 hours, split the driving time how you want to within the team - if it's teams of 4 is it possible within the timing software to allocate all 4 people's cars/transponders to the same team? Keep an eye on things but leave it to people's honesty not to run two cars on the same lap - then each person could still use their own car - one pits, the next person sets off, meaning that someone's personal car isn't getting battered for the full race, and if you do have a breakage, once the car is recovered to the pits the next person can set off...
Also, each team could have at least one marshall on track at all times - that could be the team's own marshall point for the whole duration so easy to spot if they are not there - few laps penalty maybe?? All in the spirit of a good laugh of course, which is what this should be about
Sounds cool