Reading this makes me sad too. As you write:
"He is weak, fatigued and losing weight"
I have read that CBD/Cannabis oil can help against these symptoms. One man gained four pounds in three weeks again.
"There are no other treatments for him to try"
If you want to try further treatments, maybe you can take part in
one of these studies reported by Allen. These will not cure but may extend survival for some time.
George