grandparent rights

My mother and my husbands mother are both people we don't want around our children. His mother has said things like "I hope your child dies." "You don't deserve to be parents." Her husband has threatened to kill me, although I have no proof. My mother was there for about 7 months of my daughters life because we lived with her. She was EXTREMELY abusive when I was a child. I was not comfortable allowing her to be part of our lives so we moved. She then hacked into our iCloud accounts and was reading our texts, seeing our calls, our pictures, that's how she tracked us down. She showed up, took my daughter, wouldn't give her back so the police were called. She's crazy, she claims that we are unfit parents. She tried to get my husband arrested by sayin he beat us. But, they have been careful about making sure we don't have proof. 
Recently we found out they are both trying for get custody, or at least "grandparent" rights, which some people can get. We are trying to figure out how to make sure they have nothing. Any advice?