Yet with my son and I who she lives with see how she's deteriorating. My brother since my diagnosed tells her she doesnt have Alzheimer's, he's in total denial. Yet she's had it for over 8 hrs, he only sees her at most a hr or 2 a couple times a WK, I have to work full time then come take care of her. I deal with her waking me up all night long cause she Dont sleep she has cat napped while I'm working, when he comes by she's as sharp as a tack
You see it and know better, no matter how much denial others have. Been there. People are afraid of that which they do not understand. He will have to come to grips with reality, hopefully sooner than later.
Your Mom is happy and alert to see your brother because he has a whole week of things to talk about. He's not busy doing housework, cooking or laundry while he is there. She gets his full time and attention to socialize.
So that tells me maybe your Mom would benefit greatly from going to a senior center once or twice a week. That way she can be around people of her own generation :)