100% disabled AF vet travelingll by motorhome. I know wife and i can us the RV Park but can Brother in law in his own motorhome also stay here?

Yes, you can back anyone. You have to make the reservation AND PAY FOR IT. Of course, they can reimburse you but you are responsible. We've done that with a couple of our friends.

Pretty sure it's just ID card holders, but call to confirm.

Call them and ask