He is going to have to rely upon his doctor(s) to make their best judgment call on the safety of sexual activity. Hopefully he has one doctor with specific knowledge of his conditions, history, medications, and current health, who will be able to give him, and you, the answers you're searching for.

I don't think anyone who hasn't examined him and has all of his medical information should even think about advising you of his capabilities for any physical activity. I don't see how they could.

It's obvious you care for him because you want him safe, most of all. Please ask him to talk with a doctor who is aware of all these things and coordinates his care and medications. Perhaps you can go with him and try to get answers and receive some guidance. They are good and thoughtful questions.