What can my family do to save my aunt from her husband

My aunt has been married to this guy for 28 years. From that day till now they had nothing in between them as he is "not capable". For 28 years he's been torturing her mentally and now her life's at stake. We have no idea what to do.we've fought with him several time asking about this and he would say "its my family who are you to interfere here". He's giving her tablets other than the prescribed ones. We also have eye witness for this. And also he won't let my grandmother to talk to her own daughter. And without our knowledge he took her to his hometown. This happened recently when we asked about this he disconnected our call. He won't let us see her or talk to her. For all these years we kept quite because he used to threaten us when ever we raise our voice or humiliate us. Now that he's in his hometown, his sister is also involved in this. Using my aunts money to build there homes and also we think he is involved in witchcraft for years. We don't know what to do. My aunts sufferers alot and we could see it from our own eyes but couldn't do a thing.