Leaving the two at the trail heads will cost you about $10 of gas and take about an extra hour and a half of your time (maybe more if you stop for supper and a beer in Lone Pine). Its worth skipping the aggravation and time lost, and coming down that last day, you will appreciate something very very close and dear to your heart parked a couple of hundred feet away.
While arranging the shuttle, be sure to pick up any stragglers on the road.

You managed to get both cars all the way there so that you could have a shuttle. Might as well luxuriate in the opportunity. They will probably be safer at the trail heads anyway.
But that is nice that you are offering rides for those that probably couldn't make it.