I agree with missbunny, that you should simply inform people that the block of rooms is available and let them negotiate the arrangements on their own. Aside from the liability issue, another reason to do it this way is that it spares your group the trouble of coordinating the shares and collecting the money. Let the fans book and pay for the rooms directly with the hotel.
I think that’s almost it. I’m not too lucid today, so let me try again:
There are four slots to a room.
You buy up slots. The collection of slots you buy are treated as an indivisible unit. You can fill them up however you want - with friends, lovers, anyone - or leave them empty.
If you don’t buy up all four the slots in a room, then the remainder can be bought up by others looking to get housing.
So if Sally and her little sister buy only two of the four slots, then there are two slots that could be filled by anyone. Say Mr. Perv buys two slots as well, but it just so happens that every slot is taken except for the two with Sally & co - the system would want to place Mr. Perv in those empty slots. The question then was, are we liable for placing Mr. Perv there, or is it up to Sally to either a) buy up the whole room or b) act as chaperone?
Obviously we’re trying to avoid the situation altogether. I guess the broader question is if we are liable if anything bad comes out of these pairings - like unwittingly putting a thief in a room, etc.
In that case, the simplest and safest course of action is for the organizers to not deal with any unit smaller than a whole room. If Sally and Sis together want half a room, then they need to on their own find someone or someones to take the other half, before they tell you anything about it. If they can’t on their own find anyone to room with, then they have to buy the whole room. The absolute most I would recommend for the organizers to do below the whole-room level would be to make available a list of people who are looking for roommates, but let the attendees decide on their own whether and with whom to share.
I think you are still going about this all wrong.
You can’t have it both ways: you (the group) can’t say that someone can buy a whole room and fill it however he wants AND say that if someone only wants two “slots,” then “the system” would place a potential Mr. Perv in an empty slot in the same room.
Forget about slots. As Chronos said, treat rooms as a whole and if people want to match themselves up, they can do it BY THEMSELVES. People can find compatible roommates and then book and pay for the room themselves. The group should have nothing to do with organizing who stays in what room, since the guests are paying for it themselves.
And yes, if YOU place Mr. Perv in a room with anyone, who has no choice about who they get stuck with, and Mr. Perv does his pervy thing, I think you are going to find it very, very difficult to fight that in court. Not to mention the horrendous publicity your group will get.