What can be done about a step parent being way out of line?

My ex and I have joint custody of two children. My ex's wife filled out the children's school registration form and put herself down as having custody with my ex, she put me down for authorized pick up. She also put a wrong phone number down for me to be contacted in case of emergency. She signs the childrens school papers including consent for health screening. She has told my ex to tell me that our son's Dr. Apt. was canceled. When I called the Dr. office they told me it was not. My ex does whatever she wants so I can't ask him to help this situation, he wants me out of the picture as much as she does. He was arrested with my 8 year old in tow, he had her called to pick him up. It was almost a year before I found out about this.