Son threatens his father for his Property

Greetings Sir I am Karthik, a student from the Central University of Tamilnadu. I like to help someone who is of about 60 years old. He has one daughter and one son. Due to some problems, they both are torturing their father to sign a document for his property, which will be worth Rs. 70 Lakhs. Now the older man is very much frightened for his own life. His son even used abusive words and swore to kill him if he did not sign the documents. He is a long distant relation to me. I want to help him through some form. His son has the support of some local goons, making this a little bit more difficult. Looking for some sort of legal opinion to proceed further. Thank you.