Legal action against aunt for harassing and threatening grand mother

My uncle was married for 19 years and my aunt filed for a divorce three years back stating that she was a sufferer of domestic violence conducted by my grandmother, my mother and aunt(sisters of my uncle), my father and uncle. My uncle was suffering from dementia for 11years and my grandmother is 77ears old widow. My uncle was used to be beaten by my aunt and his son (who is now 18years old) whenever my grandmother was not at home. Now my uncle died 2days back in a rail accident and his son and aunt didnot bother to do all rituals. After requesting and begging them, his son did the last rites and has taken a video as a proof. Now they are threatening my grandmother to leave the house. What should we do now? Points to be remembered: 1.My uncle was a teacher of a government school which was given to him when his father expired. 2. A general diary was made three years back after my uncle was brutally beaten by his wife and his son. 3. We are Hindu by religion