i really hear you wanting so hard to help him, vaya. And I relate to how it might feel like if you can just figure out the right thing to do here, that will make the difference towards fixing things.
Maybe doing the right thing helps, and doing the wrong thing exacerbates, but ultimately, his choice for a better life will not be so closely tied to anything you do. Which is absolutely terrifying. But in my opinion, this is a key distinction to keep in mind for yourself, as you suffer or enjoy along with him in whatever bumps or successes he finds.
I definitely have no answer for your question; just hugs of support for YOU, cause this is so tough.