Parents harassment by sister in law

My brother married in 2012 ,everything is fine but occasionally my sister in law taunt my father that you are idiot, dump mind, she use to threat my parents for dowry case .Her mother always talk rude and says why you people residing with your child leave their house but the fact is my brother and his wife resides with my parents each and everyrthing in that rented house is of my father earned money.the rent of house is payed by my father ,the worse thing started after the birth of their child ,she always deny to give her child in my parents hand.even after for all 9 month duration she is just taking care of herself and everthing is on my mothers head all chores of household job. After my father retirement they shifted to their hometown because of my sister in law, as she got a job as primary teacher in some government policy ,willing they did this for her sake as she wanted to join the job she wants to teach . main problem arises as she started teaching on training period whole day my parents take care of child and in the eveing she used to abuse them for whole day activity ,now she is threating them for dowry case alongwith her mother who joined her in my hometown house .