Ex-Husband Mental Abusing my two children?

I divorced my husband back in 2002 over him being abusive to me and the court gave him visitation every other weekend and holidays and since then he and his father and mother has been mentally abusing them and I believe they have been putting a lot of crap into their heads.They are cutting them down,screams at them, threatens to beat them if they make a bad grade or wear make up or have anything at all to do with a boy other than family members. They are not aloud to even make a common kid mistake or even be a kid without them jumping down their throat. I have heard their father call them these awful names and tell my daughter that she was to fat to wear that shirt or skirt,so on. I recently gotten my son a hair cut into a chilly bow because its the boys style know and he wanted it and his father told him that he look like a fag with that hair cut so he wanted me to shave his hair off. My kids nerves,confidence are shot, my daughter is now pulling her hair out of her scalp including her eye brows and eye lashes and lashes out with madness for no reason, their staying very moody,irritable, a very violent toward their brother and sister. They go to their fathers which i have to let them on his weekend and they come home treating everyone like dirt, and treating their step father like he is trash by calling him names and telling him that they do not have to mind his fat a**. I have taken them to the doctor and have told him everything and he said's no he ain't doing that,its just the kids being kids, no one believes me but the people that sees this going on. So what else can I do? Any suggestions would be very helpful.ALso he stopped paying his child support a year and half ago so know i am fighting to get back child support and payments now.