Question regarding plot encroachment

Hello Sir, I am a NRI residing in the USA. We have a plot in Hyderabad and my father gifted a portion of the plot to my sister on her marriage. The original plot was registered on my father's name and my father expired in 2009. My brother-in-law encroached to our land and constructed 5 floors building. I engaged a licensed surveyor to survey the entire plot, my sister building and remaining vacant plot. The survey report clearly indicates that my sister's building encroached our land. Below are the details of the areas: 1. Total area of the plot = 520 sq. yds (per registration documents) 2. Portion of land gifted to my sister = 250 sq. yds (per gift deed registration document) 3. Building area in my sister plot = 290 sq. yds (per licensed surveyor report) 4. Remaining area = 230 sq. yds (per licensed surveyor report) I am at a loss of 40 sq. yds and when my mother tried to speak this to my brother-in-law, he said he did on purpose and started blackmailing us that he will divorce my sister and started harassing her. My sister is not aware of this encroachment and she is in favor of us. Kindly suggest the best possible approaches to deal with this issue.