One of the advantages of divorce: HIS problems are HIS problems.
If he has a strained relationship with his kids: HIS PROBLEM.
I have absolute proof my ex tried to brainwash and alienate the kids against me, but guess what? The consistency, structure, and unconditional love I give them means they don't believe him when he spews that crap, and he digs his own holes with them with his continuous lies.
If he CARED so much, he would make more of an effort to just be a good dad than play a blame game on why they don't like him.
*I* care about my kids, and I would NEVER let him brainwash them against me, but obviously your ex thinks you are all powerful here, and he's throwing in the towel and playing the blame game instead of actually stepping up the fucking plate, admitting his faults, and asking for a chance to make it up to them, and none of that would have to do with YOU.
ADULT children are allowed to think for themselves and have whatever relationship they want with WHOMEVER they want. If they've chosen not to surround themselves with people they can't trust or respect (including their father), that's their decision.
Just ignore that dumbass. No need to explain the obvious to him or send him a rebuttal article.
Your ex involving the kids in his affair is BEYOND deplorable, and it happened to me too. Honestly, I felt betrayed by my kids too for keeping secrets from me, but they were too young to understand what was really happening. But the older they get, the more I believe they will understand what truly happened. Your kids are adults. They obviously know already what happened, so no reason to discuss any of this crap with him.
Just let your kids choose to love and spend time with him or to NOT love and spend time with him on their own. And unless you actually HAVE been telling them lies, don't feel one teeny tiny ounce of shame here.
Waywards HATE being reminded of the truth and will blameshift their faults to anyone they can. Let go of the anger and turn it to eye rolling. He's a dumbass digging his own grave..