But why? And what "comfiest arrangements"? Everyone has the same - half a 2 person room and one bed space per person. (Two single beds is probably comfier than one shared double though, especially if its a small double, but the single people will likely be prioritised for those better beds).
If person A 's preference when needing to share is to share with person B, and person B preference is to share with Person A, why make them share with someone else? Where possible, why would people not share with the people they prefer to?
And why would OP prefer to sleep with one member of a couple (presumably in a double bed) rather than another single family member of a similar age and gender in a single bed in a twin room?
Or are you saying that OP should be one person getting a whole 2 person bedroom and TWO bedspaces to herself, whilst forcing someone to not have a room and have to sleep on a sofa. How selfish would you have to be to do that! One bedspace per person is far fairer than one person getting 2 bedspaces with that under occupancy forcing another person to get 0 bedspaces and no proper bed?
You keep spouting bitter, petty spite.
Everybody has to share. Everybody. People who mutually are happy to share with each other shouldn't be prevented to do so, purely to try to make them unhappy. It's the mentality of a child breaking a toy when it's someone else's turn "If I can't have it I'll break it so you can't have it" or RyanAir's seating policy, separating people for the sake of it.
Couples are getting no advantage. They are getting half a room per person and one bedspace per person, just as OP is. They have to share, just as OP is expected to.