You seems like a descent matured man who've seen the life in U.S. very well. It's so kind of you that though being here for more than a decade you still follow the Nepali tradition, culture, values in your life. Seems like you're an educated person too because if it was some uneducated person they would have directly gone and tell their friends about their kids. 

Saaj, this is a very difficult situation. As you've stated the example of one of your friend's son in Nepal and how you changed his life. That's nice of you but do you think if you applied the same thing here with those kids, will they listen to you?? I doubted brother?? Because immigrant kids who are born and raised up here think this is their country and they want to live the same life as Americans unless their parents doesn't control them. So in this case i don't think those kids will listen to you. 

I would say why don't you just talk to your friend nicely. Don't ask anything about their negative habits or something like that but ask your friend what his kids are doing and how is their study. Like you've said may be you never know, your friend might have left them free and he wants them to be as Americans. So just ask him how is he taking care of his kids and if he is not aware of any of those things than just tell him indirectly about his kids. Don't pour everything at the very first talk but just slowly tell him about their stuffs. Because here's what i think?? No matter how you live in the U.S. you're mentality will still be like immigrant and you don't want your or your friend's kids to live like American youngsters. 

Few notes for Lahure Kancha, bro try to think positive sometimes. If you look at something from good perspective than you'll find it good but if you look from negative perspective than you know the result. I am sure you've heard the famous song from Ani Choying Dolma, "Fulko aakhama fulai sansar kada ko aakha ma kadai sansaar bhanne." No offense Lahure kancha but plz don't start the fighting with me again like the way you did with saaj. Thanks. 

Good Luck saaj