Hi Lucy , I am sorry for your situation .
While we love our siblings and children there is only so much we can do when addiction is controlling them . Dec 2016 my wife and I called the police with an issue with our son( long detailed story) who is an alcoholic . It was the hardest thing to watch him being led away and he spend a whole year inside and is due for release in 2 weeks . He has told us repeatedly that what we done was the best thing we could have done as he was totally out of control .
He attends AA inside and looks like a changed man . In his words "all I want is a quiet normal life with my son" ) .
We are offering initial support until he finds hos own place but we have also laid down the rules ,if he drinks he is on his own .
You must not let your siblings addiction destroy you , he needs help and obviously is not listening to you .
I hope you find peace and a way to deal with this