Dowry harassment by my mother, sister and her husband.

In June 2015, We got married and were staying in Chennai along with my mother and Grandma. In the initial stages, My Wife used to blame my mom and will narrate the things what has happened at home when iam not there. She conveyed that my mother demanding dowry from her when iam not at home and at the same time she used to say that my sister and her husband forcing my mother to demand the dowry from her. I didn't believe Initially but as the time pass on I saw a series of events which my mother and my Sister did against me and they all started to demand (through a letter) me a lump sum amount. We don't have any audio/video records on such instances. Infact, I was the eyewitness when my mother abuse my father-in law and their family in front of her and also we have enough evidences of the letter we wrote to them regarding the harassment and they didn't reply and they didn't deny the facts. Further, she has given them one month pay without my knowledge and my mother also dint convey me. She has been threatened not to reveal me. During Feb'16 my mother fought with us and got separated and living in my Sister's residence till date. When she left she took my Grandma (aged 87) along with her to my Sister's residence. My Grandma handed over her original parent documents of her independent house and still it is lying with me. However, In the month of April 2016 the residence was suddenly transferred into the hands of my Sister as a gift deed. As per my Grandma's wish she wants me to gift her chennai residence to a charity or else to Government of India for a cause. Though my Grandma is under their control, my call was denied and couldn't able to connect her for such urgent transfer that too for my Sister though my mom is alive. Later, I received a text from my sister around 1.29 PM on 27.07.2016 stating that my Grandma was passed away on the same day at 7.00 AM in the morning and her body has been donated to a hospital in chennai as per her wish. Me and my Wife family rushed to the hospital and saw my Grandma's body. On the next day, I received a 20 Rs. stamp paper dated 22.06.2016 from my neighbourhood and the stamp paper posted date was 25.07.2016 stating that my grandma is in need of money and she demands 24 lakhs for the amount he spent for me in purchasing plots in chennai in my name (In the name of Grandmother letter was written by my mom). However, in that letter it was a thumb impression received on 28.06.2016 and she very well knows to sign although she is uneducated. As such, her death is still a mystery and they are not in a position to reveal the medical treatment that my Grandma underwent for her illness. At later stages I researched and found a letter from my Father (died in Sep'12), which was kept under my mother’s custody for a long time. In that letter my Father revealed that my mother has received several lakhs of black money on sale of her residence. As such, my Grandma is uneducated and unemployed how come the source of income be funded for her residential property in Chennai? Further my father revealed in his letter that my mother and Sister has made several murder attempts on him and he has been escaped in all such attempts. On that time I was a student staying in the hostel. Now, Me and my wife face the similar situation as my father underwent from them and now they wrote a letter to me stating they need 3 equal shares in my father's property which are plots and 1 individual house in Chennai outskirts. Please suggest me. Me and my wife life (who is nearing her delivery date) are at stake because of this dowry and property matters. Also I want to fulfill my Grandma wish which she dreamt of gifting her chennai property for a charitable cause and the same was embezzled by them. How Can i proceed further in this case.