I would kindly go over to them and ask them to please move their car. That is of course if you need to get in or out. Then I would talk to your neighbor if he would please tell his friends and family that this is a shared driveway and ask them to reframe for parking in it.
Now if that fails... when you see them there walk over ask them to move drive around the block come back and park were they were...lol And make that neighbor come and ask you to move!