Suicidal threats

My elder brother has been abusing my parents from past 8-10 years. He started giving suicidal threats when he was not able to find a suitable match. He is married now though since last 2 years. Now my sister in law, ever since she started living with us (me, mom, dad and elder brother), she never talks much and seems like depressed. They have a baby now. Two months back suddenly she started behaving as if we all (including me, mom, dad and elder brother) are going to kill her, we have installed cameras in her room and all. My parents never even shouted at my sister in law. We felt she is mentally not well. So we told her to stay with her parents for couple of months. Now her parents are saying like "Kisine kuch khilaya hoga". We don't believe on these things but they are threatening us that we are responsible for her illness. But she has been behaving like this ever since coming to our house. On advising my elder brother to stay with her wife alone for some time, he gives suicidal threats. How do we handle the situation? I want to protect my parents from my elder brother's abuses and suicidal threats and the same time prevent us from my sister in laws parent's threats about "humne kuch khilaya hoga". Should we go to police for protection from my brother? Please help. Thanks.