If those bills also include the rent, it's absurd that you all agreed to pay the same despite having access to different facilities. There is no friendship in financial transactions. You're cheating yourselves. If someone is getting their own toilet, they should be paying more than someone who isn't because that would be a fair market split. That'll also eliminate most of the arguments and feelings of unfairness. The ensuite rooms should cost more than non-ensuite rooms. The bigger ensuite room should also cost a little more than the smaller ensuite room. That is how pricing is done in student halls. Whoever is willing to pay can take them, or settle for the rooms with shared toilets.
If the rent isn't included, write down the rooms on different pieces of paper, ball them up, toss them in a bag and have everyone pick. Whoever desires someone else's room can then discuss with that person and settle it between themselves.