Divorce under mental cruelty

Hi All, Thanks all in Advance. This is about my sister's life: I have a younger sister who got married to a Government servant in 2011 June, my brother in law and her family used to harass her as because she is not becoming mother up to 7 years. But after lots of struggles and prayers they have two children now, one baby girl 2.5 years old and one baby boy 8 months old. There was some argument happened between my sister and brother in law and they left her alone at home along with her two children and went away from home. as a parent my father has called them many times to talk but they did not responded at all,and after waiting for 3 days my father brought her home and we gave a petition in the police station a they have not answering the phone calls. The local S.I called them to the police station and he tried to compromise both my sister and in law's family. after couple of sittings my brother in law compromised and told SI that he will take my sister after two weeks of time. But it is been one week ,and my sister has received an SMS about a case filed in court law for divorce under mental cruelty and apper for hearing on Feb 3rd 2021. we have given petition in the Police station but we have not filed any FIR against him or his family. and S.I are saying not to worry but we are tensed about getting SMS. She does not wanted Divorce at all but he has filed divorce in the court and he cheated her many times but still she wanted to live with him. Even he cheated Police as well by saying that he will take her after two weeks of time and when SI called his lawyer he also said we have not filed a case which is not true. so what is the best step we should take at this point of time. Please suggest a best step so that my sister should get perfect justice. She has been struggling from 10 years with his family but still she wants to live by thinking of the children.but that fellow is doing all this nonsense. Please suggest best solution. Thanks, Sagar Bazar.