I think you are blaming the wrong person here, it's your DH's reaction to alienation that has caused YOUR problems. He didn't have to "be in a funk" for eight years, just because his son wasn't around on holidays. And he certainly didn't have to yank the kid from the only home he's known and force him back into your life.

Not to say alienation isn't hard, we went through it too - but your DH could have dealt with it in a healthier manner.  I'm glad you are not sticking around for the sh!tshow this year.

I cannot fathom what has been done to your SS. Your husband has made some poor choices when it came to his child. His son BEGGED him to sign the papers necessary for his citizenship in his mom's country, promising to restore their relationship. Your DH refused. And now a 17 year old, living with his mom for over 8 years in another country and culture, has been forced to return (to him) to a strange country, moving in with literal strangers, leaving behind his family and friends and everything familiar to him. I recognize there was Parental Alienation by the BM but in the end, no one gave two thoughts about what this action would do to the kid. He's angry and rightfully so.

I'd be doing everything in my power to get this kid back to his home country and his mom. 

I'm sorry you and your kids are stuck in the middle of this mess. And I'm really sorry for what has happened to your SS.

This is what happens when people are more concerned with winning at any cost. This situation is not a benefit to you, your kids or SS. The only person coming out on top is your DH because he's finally "won" custody. But what is the point if everyone is miserable? I hope he realizes his mistake.