Welcome to SR. I am also sorry you lost your older brother.
I was thinking that if you try to put any kind of 'hold' on his money, it's just gonna create problems.
You can't, and in my opinion shouldn't, try to control his money. Besides, the 'brokest' of addicts will find a way to do their drugs.
I would just focus on you and protect what is coming to you.
This phrase always sticks in my mind: "Let go or get dragged"