Non-custodial parental rights

My husband has 2 children (13 and 10) from his previous marriage. He and his ex-wife have been divorced for 8 years and she has custody of the kids. He has standard visitation. What are his rights as far as filing for joint custody or filing a motion to enforce visitation? She has been keeping the kids from him and causing many problems. He does not want to go to court, but he has tried everything to work with her for the sake of the kids. She is completely irrational and has put the children in the middle and she will no longer communicate with their father. She has also placed unrealistic demands on him simply because she is unhappy. We have a wonderful relationship with his girls and we are a happy family when they are with us every other weekend. They are our lives and we love them beyond words. We are afraid if we do nothing out of fear, we will not be doing what is right for them. We have drafted up a letter that we intend to send to her regarding all of these matters. But before we send it, we want to be sure that we are not shooting ourselves in the foot. We want to be prepared and educated on what his rights are and where to go from here. THANKS! - Is this your question? Add additional information