Marriage Issue

Hello Respected Sir, I want to ask question on behalf of my brother.My brother and mother is totally mentally disturbed with the behaviour of my sister in law. They got married on 29 april 2017 with in two months she start fighting with my brother with no reason . We have full furnished 3 bhk flat in high locality but right now brother is earning less then her. Even we dnt ask any single Rupee money n in gift we take girl as it is and as per tradition matters. Nothing else. Still sister in law coming from very poor background as compared to us but or family doesn't believe in such stuff. My mother is doing everything irrespective she has Operated her back n legs. But sister in law doesn't do any single house hold work no contribution. Just fighting and one day last year she call police with no reason no harrassment and his brother also came at our house and start abussing as he is working as a clerck he came on duty. He start abusing my mother n brother in that course my brother lightly push him and said keep quite he just fell abit on floor and he also start creating drama that u push me on duty i will complaint and meanwhile police also came they both sister in law n her brother keep on threating police i m on duty file complaint So police have to force fully with out reason no issue nothing they created fake issue and send my bro and mother to police station whole area knows hows oyr family is. Now again last month she got pragent and her family n she keep on threating my mother that we will again make police complaint .my mother is not well still she is doing everything for her. And there parents abuse my mother n brother. What we can do . My mother is very tense n so brother without anything somebad happen or false alligation. She just earn 20 k more then ky brother and Even don't do anything. What we can do help and threat us i will kill my self n keep a note so u all go behind bar. My mother is like 62 n crying n praying god . where this wrong minded girl came our house and threat i will spoil everything in false aligation. what we can do