I mean we don't really know all that. Just that she's allowed to stay at the prep house. Obviously the main theory is because of who she is, but we don't know why. It could be that the Royce family owns all the land the campus is actually on, so the main houses and the school pay rent to the Royce family. So Jill is just staying on property her family owns outright. It's also possible that Stephen allowed Jill to stay at the Prep house as a favor to the Royce family, getting a bit over them in such a way. Honestly could be almost anything DPC wants it to be.
ATM all we know is how much others are impressed by the Royce family, and that there name is on the door. But we haven't even meet the parents directly yet, so we have no idea what is going on. Your summation may be right, but it's not a fact yet.
As far as Maya and Josy, I don't see any reason they aren't going to be allowed to stay in the HOT house.
It should be remembered though, that the campus is supposed to be "dry", yet they have parties there all the time. So whatever the rules are, we know they're broken plenty of times so long as no one cares or is willing to actually enforce the rules.