I don't know exactly what anyone in this family has or hasn't done and it's hard to take any of their words at face value... With that said, assuming AM has had a drug problem for 20 years and if (IF) the attorneys can be believed when they say it's the first time they've ever seen AM sober, I cannot understand the brother saying he was shocked to learn AM used drugs.
In trying to empathize, I guess I can understand that the family wouldn't want to broadcast that he's an addict. I don't know if they are still trying to maintain the family's 'upstanding image' or don't want to admit they looked the other way. If he has an issue with drugs, it is so beyond the time for them to intervene, to be honest with AM and honest with themselves, stop enabling , stop excusing, and start reflecting on mistakes made, crimes committed, etc.
You know, if it helps AM, his family, his lawyers to attribute his past actions on drug use and that allows him to start to come clean and do right by the people he's hurt (financially and otherwise), so be it for now. It is the continued denials, straight up lies, the preoccupation with controlling the narrative that leads me to believe it is deeper and /or that they are maybe not capable or willing to be honest and that leads to WHY.
sorry, just my musings.