Pale empower I'm so so sorry. Rant coming...I can't help it!
Will these jw " carers" have access to him in the hospital? Hope not, so the poor chap gets a break.
I urge you to reach out to his Consultant psychiatrist and fill him in as best you can with whats going on.
If your family are in full on shun mode I wouldn't mince my words - when your mother said "he's made a promise to Jehovah" I would tell them, if your brother is being guilted "No! He's made a promise to a publishing corporation" and tell your sister straight out you don't believe in obeying "some random dead guy who made these rules in order to sell more books for his publishing corporation". Don't feed the monster and let them guilt him more, tell them straight this cult is what's killing him, along with many others.
I might be tempted to give the hospital some info on cult programming by Robert Lifton but they might think you are telling them how to do their job.