We don’t know his legal situation, mental capacity, advisors etc. You are assuming it’s AE alone, u don’t trust her, assuming he can’t make any decisions, but you don’t really know.
You are mistaken about disabled rights. Each person has differing abilities, and about choices they can make. People don’t lose the right to make any decisions due to disability. His abilities, advisors, mental capacity, financial situation are his own business. He is allowed to make mistakes, make poor choices within his decision making capacity. Think about it. Don’t just write-off people because they are different. He can decide what he wants to buy with his own money, he can decide where to go, what movie to see, he can decide to a park. Poor decision would be going on a rainy day. Or buying a TV that’s too big. He’s allowed to make mistakes like other people who make mistakes and poor decisions all the time.
He might be able to decide that he wants to participate, to been SEEN as a person who has something to say. Don’t deny him that. Don’t decide that based on your idea of disability that he does not exist, doesn’t deserve to be seen.