H.P.
Oh, my, you have said a mouthful...and it sounds very similar to my story. My husband's ex isn't remarried; she's convinced that I'm the one who's keeping them from being a family, and she's taught her son that. Needless to say, the little bit of time that we spend together doesn't seem to be enough to make any real changes, and we usually notice a temporary difference. I've had to be very careful about how I approach my husband with suggestions for his son because I don't want it to feel like a personal attack on his parenting. (Because he grew up with little to no parental supervision and turned out to be decent and loving and productive, he's not comfortable enforcing discipline in his children. Of course, I am a pretty strong disciplinarian--though lots of fun--so that makes me the wicked stepmother.) We've had to bring in third parties to modify for his age certain techniques. The fact is that this boys' biological parents have failed to give him certain tools, and they are now seeing the results of that, and it's heartbreaking.
If your husband is open to your suggestions, then I think that it's okay for you to touch on what you see as the root of it, only to show how it looks when you start out in a certain way because at this point whatever you do will have to be more concentrated because you have less time to make it stick. It's like he'll have to be untrained and retrained, if you will. It's beautiful that you have your husband's support in that.
I can refer you to a therapist who specializes in the challenges of teenage boys in today's world. He might be able to offer some guidance for some of your ideas.