Last point and then I'll bow out...we were talking about this in AA last night (not your BIL, just the way we put cart before horse sometimes). That we run round trying to fix ourselves and our issues, thinking that is why we use, it's a symptom, or a medicine, so if we sort that out, we'll have no reason to use.
The problem is, while that might have been true in the beginning, by the end we use because we use. We cross a line and are physically and mentally dependent, even if life were flowers and rainbows. And the mere fact of using makes all the other issues worse because it deepens our lack of worth, our self loathing, our sense of inevitability and doom.
So I tried to write a book, to see endless therapists and psychiatrists, to change my medicine for depression, to unearth and seek closure on various traumas...
But at the end of the day, we need to tackle the addiction first. To get clean, and not just for days, but for months (a heroin addict's brain will take 1-2 years to revert to 'normal' settings in terms of producing enough dopamine again to make the addict able to do the things that make them happy). With that time comes clear thinking and perspective. Then we can look properly at our issues and sorting out our lives and finding a sense of purpose. All of that is tackled in the 12 Steps too.
And what we tend to find is, miraculously, with clear heads and consciences, a lot of those issues seem much less overwhelming than they did when we were using.
In other words, and you know this anyway OP, he needs to tackle the heroin first, and then courses/jobs etc come afterwards. But to tackle the heroin, you need to detach with compassion, and let him hit his rock bottom. Give him the painful, but positive, gift of desperation.
Good luck. To you all.