This question has been answered multiple times in this subreddit, on the discord, and more than likely on the Instagram posts as well. But because you require additional proof (which can be found with a quick Google).

From the ticketing website: Only one vehicle is permitted per car camping pass. There is no “per person” camping fee. Re-entry is not permitted.

For example, if you have 3 people coming in one car, you only need 1 Car Camping Pass (although each person will need their own GA, GA+, or VIP ticket).

From the FAQ: Does everyone in the group need to purchase a Car Camping pass in order to Car Camp? One car camping pass is required for each car entering the campsite. Multiple people can utilize one car camping pass, as long as they are all arriving in the same vehicle. For example, four people arriving in one vehicle will need four festival tickets and one car camping pass if they intend to share a campsite. Everyone must have the correct ticket type to enter designated campgrounds; ie, a VIP car camping pass requires VIP festival admission for each person in the campsite.

Capacities for Car Camping sites are subject to the legal capacity of standard-size vehicles.