Modifying custody in new state

My original ordered was issued in another state. I am seeking to modify custody to be granted legal custody new state. We currently share joint legal and I have sole physical. Ex left marriage 6 years ago for mistress and has become a nightmare every since. He mentally terrorize our 7 and 8 year old children who are afraid of him. And he combats every decision made for the children. If I take children to the doctor, he takes children to the doctor in his area to ensure my doctor and his doctor are on the same page. If I take the children to the dentist, he takes children to the dentist in his area to see if both dentist are on the same page. My daughter is in need of orthodontic treatment. He called the office and told the staff not to move forward with treatment until he can confirm an orthodontist in his area will recommend the same treatment. Everything I do, he attempts to block throwing around the "joint legal custody" piece. He terrorizes the teachers and whomever else the children interact with so that they understand his role. I feel it's in the best interest of our children for me to have full decision making authority. How likely will I be able to granted this?