I'm kind of curious and so I have to ask, is it possible that she is on the spectrum too? It sounds like she might be since the symptoms of those disorders mirror some of those in autism.
Now so far as what to do, that's a difficult question to answer. If it was just about you then the answer I have is to make a safe place for yourself in the apartment that you can retreat into and finish what you need to do to graduate, then get out. However, this is also about your brother and mother. Now, if your mother is on the spectrum, you may be able to qualify for some sort of aide to come in and help keep things organized. With two or three autistic people living under the same roof, this might not be a bad idea if you can find the help. The problem is going to be getting through her rigidity to let someone provide the assistance. Well, that and finding someone to provide the assistance free of charge. You might want to see if there is an autism charity or government program you qualify for to provide this assistance.
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Uncertain of diagnosis, either ADHD or Aspergers.
Aspie quiz: 143/200 AS, 81/200 NT; AQ 43; "eyes" 17/39, EQ/SQ 21/51 BAPQ: Autistic/BAP- You scored 92 aloof, 111 rigid and 103 pragmatic