You negotiate? Did you not discuss the rooms set up when you had first viewed the property and think about who would have which room? (I mean, I assume not, since you are about to move in and don't seem to know which actual room you're moving into).
I'm also not sure how 'far away' the bathroom can be in what must at some point have been a two-bedroom house, but the fact that you are describing it like that, perhaps indicates that you don't particularly want the ground floor bedroom, which would at least be a starting point in your negotiations with your housemates. With any luck, one of them will want that room - in our younger son's houseshare last year, one of the group asked for the downstairs bedroom straight away when they decided to take the property.