Harrasement by brother in law

Hi Experts, I need some suggestion , This is related to my sister , she got married in april 2007 ,both are working , she has two children one boy 8+ yr and girl 7+ yr, we all belongs to jaunpur city that is in U.P. after many problems and hatred from in laws side , she managed to stable there in lucknow. we (me n my mother ) always helped her for any problems. My "Jija" has habbit of "masti and aishbaazi" , so we have to help sister in any case (Financially, emotionally etc. ) Problems were always there but actual problem starts in year November '14 , Jija lost his father in road accident, so his mother wanted him to live him with them , sister asked Jija to take her to Lucknow , so she can take care of everyone ( kids, Jija n mother in law) but Jija's mother was not ready . so one day a argument turns into fight and Jija beats up sister badly in front of my mother and my wife. (we were there to support sister as jija was not living there since long , sister couldn't live alone as it's very risky for single person with two kids in lucknow. You all obviously understands how tough it is to for a single working mother whose children are minors and just started schooling and worst is she started facing problem at her job , as she has to take off for her family duties. Slowly different kind of torture started from Jija and his family , in spite of helping her they started giving mental torture of taking divorce, adoption of childrens, defaming her , taking her all money , ( they even took home gas cylinder ..:( just imagine they are at their lowest point ) defaming me n my mother . all types of torture, we were bearing all this patiently , as sister was not ready for divorce , so were not left with any option. whenever he comes at home he comes with a new torture idea, regularly beating and abusing her, when it doesn�t affected her they started abusing my late father , my mother , we were listening all this but did not take any action as we can not make our life more worst, ( we have some other issues too those isn't relevant here so not discussing) . Now it's 9 yr for their marriage , my Jija was waiting for this i guess as i know there are some laws related to this. he said today to sister that i have sent one notice to your mother's address from court , now we don't have any clue/idea what is this notice is all about?? shall we accept that notice or not ?? if that is for Divorce then how to proceed?? ( my sister does not wants to give divorce) or may be he is sending notice for domestic violence against my mother as he use to say that your mother and brother are intervening and your mother beat me up ( which is totally lie , my mother was protecting sister when he was beating her ). after he beats sister 4-5 times and gave life threatening statement like i ll kill you , so i suggested sister to send a letter to city SSP so that it should be in their knowledge. Police men visited her, took some money and settled the things without any action. Now we are clueless what to do. Sister is very courageous but don't want to give divorce. She says All will be Ok one day. she is trying her best , even i was sometime fed up but we have to support her in any case. Our family scene is very bad . I am living in Delhi alone, my mother is in Jaunpur alone ( it's also a threat as Jija and his family lives in same city and they are socially very strong as they pretend ) ,Sister is in Lucknow alone with Two kids, we visit there regularly in fact last 9 yrs we are always there whenever required ( and unfortunately that need arises regularly ) we are not very social, straightforward people we are , don't know how to manipulate people or things. Please suggest me how to proceed now, Shall we accept that notice , if it's related to divorce then what to do ? and if related to any other defamation, domestic violence thing how to tackle. I am ready to do anything , now i have to lead from here, sister has done a lot but this marriage is not going to work . I want to restrict them somewhere somehow. Pls suggest. Thanks and sorry if its too lengthy , and for my bad english. P.S. I had written this 2 years back, anyhow sister tried her best to make things working but its worst now. Writing the same letter with some modification. Please suggest a good lawyer at lucknow.. Now we want to take all strict action except divorce. Regards