i think it would be very difficult for anyone, including you OP, to really understand what is going on with your brother without professional input. A differential diagnosis for ASDs is schizophrenia, schizoaffective, or other psychotic disorders, so really it's anyone's guess at this point what is truly going on.

I would be hesitant to place ANY label on him at all unless there is some professional involvement.

I would recommend therapy for yourself and since you haven't disclosed the details of the estate issues [I'm not asking you to], perhaps look into what rights you definitely have or could possibly before things disappear for good. Regardless of any specific mental illness, your brother is likely in distress and from his POV probably just doing exactly what makes sense to him... but that could turn out to be very very painful [as you already know].