My understanding is that there can be more than one tent to a plane, but they do have to be in the footprint and are supposed to be family. Some folks up there are quite practical when it comes to these things, and I suspect that the folks that ride in with you would be fine. The folks driving, though, might be up a particular creek sans propulsion. I needed to get some info on North Forty camping just now and asked about HBC while I had them on the phone. It turns out there is no associated car parking, and there is no overnight parking in the normal parking lots. Camp Scholler has an overflow parking lot for folks that don't want to leave their cars on their campsites that might be available, although I'm not sure they would allow that for HBC. Likewise, if one were to register / pay for camp Scholler, they might not be allowed to set up in HBC.
My recommendation would be to just call HQ and see what they have to say about your exact scenario.