I am the nominee for my Father's bank account but my brother is demanding to give his money to him

I am from Hyderabad, my father is a retired railway employee and gets pension. Now he his 83 years old and I have 3 elder sisters and 2 elder brothers. My father lives in my eldest brother house. And I am made the nominee to my father account by my father after my mother passed away in the year 2016. Since then I am his nominee, and last year that was 2020 February and my father was admitted in the hospital. He after being discharged ce to live with me. Then my father gave the cheque book, atm card and password along with his medical cards to me. My father said that my brother and his sons used to withdraw the money from my fathers account and steal them which was later checked in the bank statements. My father is almost in his last days, and losing his memory too because he lives with my eldest brother now not giving proper diet as he uses black magic. And now he is demanding by threatening me with dire consequences to give him my Father's bank documents and atms. He is torturing me and my father in his house by not giving proper food. Please help.