Bhabhi's violence against my family

We are joint family. I am a daughter unmarried living with my parents and bother's family. he has wife and 2 kids. my parents and brother are not educated so i have always guided them in lot of things as common living. Now my bhabhi's even though she say he is BA graduated, she is still unable to understand many thing. it all started when i found about her kids are ADHD symptoms reported by school they are studying and she abuses me, my parents, her husband and even we found she emotionally backmail her own kids against their father, and in laws and now including me. we started the treatment for elder kid for ADHD and SLD but it is such a sensitive matter as he is expose to phonography at this early age 13 years of about that she knowingly support kid and doesn't want to inform us. we got to know from sources from school. We as a family are facing this issue from 14 years since my bother's marriage and since due to work i was away and last years i came an staying with parents. its so difficult to live with this lady as she create nuisance by herself everyday with my mother, father , me and brother too... for irrelevant matter which are not important. My brother earns very less to fulfill the need for his family. as per our grandfather's request we support him in all terms so that his kids go to school, study, wear good clothes, my parents and I showed all love towards kids for their betterment. but despite of this support she carry's all emotional abuse with us definately we also sometime react towards to answer her but it is so anoying with everyday. There are so much to it that I cant even write full that how much we are depressed, lot of health issues on my parents and bother is also depressed and stressed due to this. My parents are in their 70's I myself is elder daughter in 46 years never married....(concern here is not my life its my parent's life, i will get job and will stay but they are older and she treat my mother as servant as she know my mother will do it somehow. I am scared she can harm physically by emotionally blackmailing her kids or maybe by herself). My bother says he cant'[ think of divorce coz she can ask for heavy alimony and he doesn't earn much to give her that alimony. we feel so stuck. Can anyone guide us please?