Threat On In Laws

My sister in law is a threat to my parents both my parent are a heart patient and my mother is handicapped. I will be married in a year and will have to move to Gurgaon along with my husband. My sister indirectly tries to harm their health. As she knows what is harmful to she does the exact thing. Once she made tea in an uncleaned vessel which was kept open overnight and was not washed. If we say anything she threatens to commit suicide and put false allegations on us. We didn't bring her as our maid. But since there are two women so we divide our work equally. She chooses to cook always and i am afraid if she does something. We cannot wait for it to happen. Her father is a man with criminal background. We came to know about this after the marriage. All the laws say women are more powerful in these cases. But aren't there any help for men Even men go through domestic violence mental torture.