Is there extra parking for a 3rd car anywhere on the campground. Not within the sites but extra parking in a lot of needed?

Charge pond and Fearing pond both have parking lots but you need to get there early. I believe it's $8 per day

Yes. You can have 4 cars for 4 adults on a site, 2 can park on the site, and the other 2 have to park in a designated area in the campground. But you have to let the office know, so you can get the passes.

Depending on which site your staying look online on the site they have a map and mostly asked questions section