how do I sue for theft against a family member?

Good morning,my problem is with my brother in law.We asked him to leave because he is stealing money and anything valuable from my kids and from us when he was still living with us so he could have money to use for his drug addiction.Now he visits often and my mother in law lets him into our home.At first , he asks for food then after even our grocery supplies and broken appliances.But last week he started to ask for usable appliances and even took our extension cord when we refused to give him money.What can I do to stop this man? I am getting stressed because when he comes here and my mother in law lets him in, I don't know what he'll take especially when I'm not at home.And if asked where he took the things, he denies all and even gets angry.Please help me. thank you.