Providing Legal Right to My 69 yrs old Uncle

I'm experiencing severe difficulty in helping my uncle to get his earnings and property papers. I have three brothers, and I am the youngest of all. My uncle, who is 69 years old, was never married and has no kids. He was a farmer and worked for my father his entire life. He worked selflessly for us and never demanded anything from my father and mother. My father, mother, and uncle lived together in a village in Bihar till my mother died in January 2023.  My father and uncle inherited huge land property from their father (my grandfather). My father also has a home in Ranchi where my 1st elder brother has lived with his family for 27 years. After my mother's death, my father relocated to Ranchi with my uncle. But my sister-in-law (my 1st elder brother's wife) never liked my uncle and didn't take care of him at all. My uncle had cataracts, blood sugar, and high blood pressure, but he was never taken to a doctor for his treatment. Not only that, he was offered leftover food only two times a day—11 AM and 10 PM. She used to curse him for no reason.  My uncle has only one eye, so I used to pressurize my 1st elder brother to get his cataract operation done. But he never did that. Because they (my brother and his wife) wanted my uncle to die soon. Finally, I brought him to Bangalore and got his cataract operation done after reducing his sugar level and blood pressure. In between, my father handed over all the property papers and bank account details of my uncle to my 1st brother. Now, my uncle is asking for his money and land papers from him, but he is not ready to give anything. I want to give my uncle his legal right, but I don't know where to start from.  Any suggestion would be highly appreciated.