The second door that Bobby and Oliver knock on is clearly the Bradys' front door with a "No Peddlers" placard and interior background wall added to make it look like a different house.
At the end, Greg tells Marcia and Peter that they will have to wait to fight over who gets his room in the attic since he hadn't decided where he was going to college yet. Mike and Carol had already promised Marcia that she could have it when Greg went to college and all of the kids would get it in age order. There is no reason for Marcia and Peter to fight over it, as it had already been decided.