My Husband's 51 Yr Old Unemployed Son Is Living With

My husband's 51 yr old unemployed son is living with us. He is not getting a job and will stay in his room for 2-3 days, slipping out to go to bathroom and water. When his dad asked to talk to him he said to wait til tomorrow. He has not come out of the room. This is upsetting to me. All my children are in their own homes and doing well. My step son, Mark is hiding from reality and taking advantage of us. How to we get something done?