In middle of divorce and custody battle with my emotional abuser and narcissist.

How do you let go of the lies they are telling the judge? How do you let go of the lies they are telling your children that are 4 and 1.5 yrs old. How do you let go of the rude comments they say? I get so frustrated and emotional over the things he lies about to the judge because they are about our children. He also keeps calling our children his children and the possessiveness rubs me the wrong way. How do I stop my mind from constantly going in circles about the things hes saying even tho I am ahead in this custody battle....im struggling with this.