In-laws tortured by daughter-in-law

My father is diabetic,almost lost his vision and heart patient as well. My younger sister is a psycatric patient. My brother got married to a other caste girl few year back with out our knowledge. 2year back he spoke about his wife and son. They were staying in cuttack in a rented house. We accepted my brother's marriage, wife, son.. They came and stay in my parents house. After few month my brother and his wife threw party for their son's first b'day dispite of covid. Few days after birthday celebration she went to her parent's house. From there she went and stayed in cuttack. After several month my mother was paralyzed. At that time my sister-in-law came back. She brought her cousin sister along with her as helping hand. My mother was recovering slowly but she got covid and passed away. Within 3-4 days of her death my sister-in-law started keeping an eye on all of us. Started telling my brother against all of us. My brother was scolding my younger sister all the time and sometime my father also. I came back to Bangalore after 1-2 month of my mother's death. After 4-5 month of my mother's death my father got heart attack. After 15 day's of his operation again she went to her parents place. My father was with my younger sister and brother. Most of the time they were having outside food. She returned after 20 days and after few days she went and stayed 2 weeks in some relatives home in cuttack for some work and we see her photo in picnic and partying at home on watsapp status. Once my younger sister was preparing tea with my other sister. She kept the spoon outside the milk powder bottle. My sister-in-law was behaving very rude with my younger sister.So my other sister told her to calm down and also told as she a psychitractic patient we can't expect her to do the work with all perfection as we do and this kind of behavior will create problem for her. My sister-jn-law started fighting with her. My sister went to her hostel and informed me. My brother called after and started blaming my sister. He was talking about other version of the topic. I explained him to talk to both of them and shattled the matter. Things became worse after that. Both my brother and sister-in-law started blaming me and my sister for creating disturbance in their life. They stopped my younger sister's medicine without asking doctor. She was violent, hitting her head on wall, broke cell phone. By brother told she is doing all these knowingly. My other sister took her to hospital and followed up with her for medicine for few days. But sometime she is taking her medicine sometime not. After my father's operation my brother didn't took him for any cardiology consultation and not taking him for daibetic consultation from past few months. Sometime my father getting food on time, sometime not. Me and my husband tried to talk to my brother, no effect. My sister-in-laws cousin is still there from past 1.5 year. Her niece is also staying from.past few month. Please suggest