The best that you can do is to tell your ex that he is putting his relationship with his children at risk by ignoring the pain his new wife is inflicting on your children -- even if her intent is to protect your ex. It is up to him to define the relationship with his children. His decision to be silent is itself a decision with consequences. As for your relationship with your children, they need to know that you tried to protect them. More than that, you cannot do.