But I really don't understand this maths logic of "OP paid more pp" that keeps cropping up?
Let's take out the single person factor which appears to be making things emotive...
Say my small family of 3 (DH, me, DS) go on a group holiday with some family friends. Let's say, a big extended family of 15 called the Browns. The Browns pay £1000 in total (so about £60 pp, although we don't know how they're splitting it among themselves). My family pays £250 in total (so about £80 pp).
The holiday land comes with a nice big shared backyard. Altogether, the holiday land would cost £1250 to rent, which neither my family nor the Browns would be able to afford on our own.
There is a big house and a small house on the holiday land. Again, remember that the Browns paid £1000 and my family paid £250.
According to your logic, my family of 3 should get the big house. All 15 of the Browns need to squeeze into the small house, as they've paid less per person than us... Despite the fact that as a unit, they have paid 4x more than us, £1000 to our £250.
Makes no sense right?!
How each "buyer unit" (couple, family, single) arranges their finances is nobody's business. Someone's parents could have sponsored their entire holiday, which would in theory mean they were paying the least out of anyone there. Or one half of a couple could be paying for the entire couple, which means that payer would be paying more than any other person there, even more than OP. None of that matters. All that matters is how much each "buyer unit" (couple, family, single) has paid towards each "product unit" (room). Then the buyer unit will have to share the product unit among themselves (ie share the room).