A: Here's another way to explain this: the Brady bunch all pitch in with the baby sitting money, the paper route money, and royalty money from the TV show. That's how they come up with the rent. One of the Brady boys decides to leave home 'cause he's got an on-the-road stand-up gig as a comedian. The Brady boy sells his paper route to a kid down the block and that kid wants to move in to the boys' bedroom at the Brady house, and says he'll pick up the comedian's part of the rent in exchange for being a part of the show.
If the Brady bunch nix the idea, they'll have to pick up the slack on the rent for the missing Brady boy. If they let the kid in then they can decide how much he has to pony up to live in the bedroom, and be on the show.
Just like on the Brady bunch, your tenancy is for the entire rental premises - It is the whole house that is rented - the actual tenancy agreement isn't divided up where one person has 1/8th of the action, or 1/5th, or 1/4, or whatever. Right now you're in it together but if you decide to become a quartet instead of a quintet, that's up to you guys, as is who pays what and to whom. As long as the landlord gets his rent on time and in full you should be okay until the show goes off the air, so to speak.