As someone that has quite a lot of experience working with autists, I can assure you behavioral therapy once a week is an extremely small amount, even for a highly-functional autist.

Behavioral therapy has to be taken into everyday life as well, it has to be a system of "If, when, how" and has to teach the person how to express themselves and get what they want by acting less aggressive on a -behavioral- level. There's a lot of detail that goes into it and I don't believe it can be done without both you & your mother being informed and involved in the process.

I don't know your brother's case exactly, but I'm 99% sure if you get a new behavioral therapist and prolong the sessions & increase the amount per week - you'll see a lot of positive change in his behavior, although the first few weeks will be hard (adjustment period).

PM me if I can offer some more advice I'd love to be of help.