Yes he is in denial and your response inadvertently colludes with that as I will explain.
You have signposted him to professional help and expert information. All good. But he has rejected this, hasn’t engaged, won’t pick up the tools. That is his own journey in his own time.
But if there are no consequences from YOU then YOU are effectively accepting, enabling, facilitating her bad behaviour and his bad treatment of YOU and YOUR DS.
The answer is not to repeatedly nag and engage in some sort of tug of war game - with him in the middle - you just need to drop that rope and have a v clear and firm boundary with him. This is an action, a consequence.
It is not more decades of round and round circular nagging trying to get him to see the light. He already sees it - just wont look at it.
So YOU need to totally change the dynamic - imagine the tug of war - you drop the rope and just watch them collide into chaos.
Declare your own personal boundaries and communicate them to him once - as you would about any other abusive person (eg difficult neighbour for instance):
- He is not to tell you anything about her.
- He is not to have her on FT/call in your home in your presence.
- He is not to give her any info about you or your life.
- You will not be going to her home.
- She will never set foot in yours.
- You can decide if these also apply to your DC for their protection.
By doing this you are emotionally protecting yourself by not exposing yourself to her nastiness and his failure to protect you. It probably suits him that the grenades are hurled directly at you as he gets to swerve them.
He has chosen to date not to defend, protect or honour your dignity against his mother. If he doesn’t deliver on these then you need to seriously consider your next steps.