Need divorce guidance, custody & property guidance

I have a brother who stammers and his wife keeps torturing him and my parents for his condition. My brother has one 13 years old son. Last year, we had to send him to my sister's place, as my sister-in-law was not taking take of him well. She was involved in some extramarital afire and my nephew himself informed us about that and we also caught her on various occasion and whenever we question that, she starts accusing us with false statements. She keeps torturing us by saying she will committed suicide and my parents are old age parents (>60 years) and at times handling her becomes too difficult, as she becomes physical. Now, one month back when my engagement happened, she left the home.She herself agreed that she has no physical contacts with my brother since last 6 months and said that she will never have. The ancestral property is on my father’s name, please suggest how we can proceed ahead for divorce, as now she will create the scene again when the marriage will happen.