Well hellooooo Luke, step into the garden...
How old are you?
If your old fellow won't let you in his tent, then for gods sake don't go anywhere near Maison Blanche after nightfall.
First off, if ole daddio already has a camping ticket, then there's nothing to stop you putting a tent up at KN as well; the camping ticket gets the car in and includes as many passengers and tents as come with it. The General Entry ticket allows access on foot to most other places.
If you're old enough for your dad to trust, (then stay clear of Paula, otherwise you'll never get that glazed look off your face) and are looking to pitch up on another site, then you've done the right thing, just keep an eye on the forum. There are a few tickets on e-bay, but it's anyones guess what they'll go for.
Best of luck!
H