Epilepsy stage 4 before marriage can husband apply for divorce

MY brother got married in may 2016 but we come to know in jan 2017 a girl is suffering Epilepsy stage 4 disease so we ask her and her parents about this disease , so we come to know she is suffering from disease since teenager, so we took decision to quit this marriage in feb 2017 and we ask her parents to take her with you, since feb 2017 to till date they are forcing us in so many ways to take her to our home as it is condition but since feb 2017 to 30 sep 2018 till date she is at her house so we decide to file divorce case in august 2018 and counsilar done we said we want divorce she said she want remain marry and she filed case under section 12 against us 3 brothers and my mother. so now question is Q1} can my brother get divorce in above dissease was there before marriage but we dont have solid proof Q2} as per new rule section 497 scrapped, can my brother get married but no evidence of marriage and having a child but not using father as this marriage is not legal and dont have proof and second wife also ready to accept. Q3} is it leagal in india extramarital affairs having children Q4} on what basis she filed case under sec 12 with all brothers and mother which dont have any issue whatever happend between couple. your advise is highly appriciate. thank you