Confused here. Just checked your listing and you can only book for one person!!! How can they book for 2?
If they book for 1, and then ask to book for 2 then all you need to do is say,
Unfortunately, as per the listing, the room is only available for one person.
Should you now wish to have 2 people stay then I would suggest cancelling your reservation and booking elsewhere. When you search for places, be sure to enter the number of guests that in your party and this will bring up only the listings suitable for you.
Thanks
That's surely all you need to say? If they keep the booking and 2 people arrive then only allow the booker in and send the second person packing. Or as they have broken the house rules then you are in your right to send them both packing.