Daughter in law is making extreme problem in family.

My brother got marreid in 1999.After two years of marriage she stared to fight with brother and my parents.but we always tried to manage the situation and after every 2-3 months she again fought but its mostly with my brother and some time with my parents.In 2008 we had to file written complaint against her. because her family filed a complaint against my parents and brother.but problem is that we dont know what she want now since my elder brother got married in 2015,its very frequent and always fighting,mentally harassing my parents and brother and whole family.we knows the family values and dont want to ruin brother`s life and family so we tries to support the situation most of time and every time. most of time we keep our mouth shut so that situation dont get out of hand.but she is using this against us.thinks we all are idiots and afraid of here.she also threatens my brother for divorce very frequently. now the points- 1.parents are senior citizens (father-78 mother 66 approx) 2.both were in government job now retired and living with my brother in home town. 3.we all three brothers lives in delhi and go to home for 1-2-3 every month. 4 my other daughter-in-law lives in Lucknow as she is working there and also her home town(married with my other brother in 2015) 5.we are very peaceful person and don` want to ruin brother`s life so we are not taking any action against my daughter in law. 6. if she files against us as we are not living there in home town. should we worry about that? and what would be the impact of that complaint against us. but now its enough something need to be done. please provide a strong advice. eagerly waiting thanks ravi