Would there be a preliminary hearing to determine if a request for change of custody is valid? Would both parties be involved if there is such?

My husband was granted physical custody of his kids after their mother was arrested for fraud. She has short supervised visits twice a month. She had allowed their daughter to be sexually abused by her stepson. It was also outlined in the order that she submit to a full panel hair follicle test at my husband's request and if positive all visitation would immediately cease. A month after her release she was arrested for VOP for drug use. After serving her 30 days, my husband requested a drug test. She refused and has not called or seen her children since. She writes them about every 3 months and makes promises she never keeps. Now her estranged husband (who is not allowed contact with the kids) is emailing my husband threatening to give her money to take him to court for a custody change because she doesn't "get" to see the kids. We're not really concerned that she will get them, we just hate to see the kids go through this again. Is there anything we can do to stop this nonsense?