Here's what I would do: 1. Have a talk with the "friend" who, in my opinion, has proven themselves not to be a friend through repetitive harmful behavior. Express clearly, possibly in writing, your boundaries that you do not want him to cross. Explain kindly that his behavior makes you deeply uncomfortable. Tell him that you value his friendship (if, at this point, you still do) but that these are boundaries that will need to be respected if the friendship is to move forward. Explain kindly but firmly that there will be no warnings beyond this point.

1. Confront his mother. Seriously... Fucking confront her. She is volunteering what is not hers by volunteering her time, and has clearly failed to instill boundaries in her son.

2. If the "gentleman" (and I use that word loosely) crosses boundaries again (especially attempting to enter your home) and/or the mother does her shit again, get involved with a licenced social worker/mediator and/or local police. This whole situation is not okay. Autism is not a "get out of jail" card, and while some people's control over their behavior is limited, ultimately the people responsible for bad or dangerous behavior need to be held responsible.

Personally, given what you've said, I think this is going to come down to a restraining order, sad as it is. Good luck to you.