Yes, that's why we're discussing it, thank you :)
It never appeared to me that this doorway was to lead into a hallway. It didn't seem there'd be enough space for more than one small room back there, even if the viewer were expected to use their imagination.
And in the episode with Roxie (Dr. Thelma Butler) Lester says Mary's in the bedroom for an hour getting dressed, or something. Pearle chimes in to add: just be glad she ain't in the bathroom!
But that mysterious door is closed leading to Mary's bedroom, and everyone's sitting in the living room waiting for her to come out. So apparently in this episode, at least, this is meant to be one bedroom. Then in other episodes, it might be Brenda's, etc. Yep, a definite continuity issue!
Brendas room was on other side behind kitchen area and the parents were behind wall near front door. But I nvr questioned a 2nd bathroom for brenda or guest unless it was near master bedroom.