I've had 3 experiences with sharing a cabin. With my Sister and a cousin, we agreed sisters share the bed, and cousin had the sofa area. It worked out well. Cousin paid less than we did.
With a friend one time, and an acquaintance another, I had the bed, the other the sofa area. This was determined before hand, we all agreed, and I think it worked well. Each time, I paid 1/2.
In April, 3 of us will share a family veranda cabin. We each have a place to sleep, ( cousin gets bed, I get Murphy bed, friend gets sofa ) we each pay 1/3 of the cost, this was agreed upon. We'll see how that works out!