Seven hour drive?
Leave as late as possible. Personally...........I've had better luck with bored kids falling asleep, even teens, but then mine had early bedtimes. Still.......to cut some of the boredom........we have a good 8 hr trip home to visit family, we always started late in the evening after dinner....usually close to bedtime for the kids. Within an hour or two boredom set in and all 3 were asleep which minimized stops (made the trip faster) and bickering.
Didn't have much bickering like that (and we had a little car)..........that sort of nonsense was cured before they were school age.
Helpful hint: if the "space" issues start to grate? Crank up your radio to music they can't stand but you think is just fine........and I do mean CRANK IT UP 1. you can't hear them and 2. they will stop, if for no other reason than to get you to turn it off.