Call the school, let them know that he has other offers he's seriously considering accepting and would like to know how interested they are. "Come up to a camp" can mean a lot of things ranging from we like you and want to get you on campus to offer, to we want another look for the rest of the staff to see, to we want your $250 so we can pay our volunteer assistants.
So if they say come to a camp let them know you can't make it. If they don't offer to have him come up and visit to see the school - they're not interested. When you have offers in the hand you don't need to be dishing out money for more camps, hotels, etc. I would say that unless you feel an offer is coming there is no need to really set foot on any of these campuses unless it is a huge upgrade academically.