One option your friend could take if he decided to leave some money to the drug addict could be to put a clause into the will that the gets a reasonable amount but it's drip fed to them.
Another option is the addict gets drip fed for 2,3 years or whatever but has to pass 6 random drug tests over each year, if they fail they forfeit their share to their siblings.
Option 2 is a cracker
The people leaving the money can die knowing that they gave the addict one more chance to redeem him/herself even if they don't deserve it and the courts will have a great reference point if the will is contested.
I am assuming that most people who have worries about their will probably have a reasonable amount of assets.
Note. I'm currently an executor of an estate with a third party throwing lawyers and the kitchen sink at me because they want control and IMO the chance to strip the estate bare before the beneficiary is old enough to receive the inheritance.
I'm in the process of handing all of the estate over to the public trustees as it's the best option of a group of bad options.
