Brother and his wife are not ready to give property papers to my father

My father is a senior citizen and penalized for the last 2 - 3 years. After this situation, my younger brother and his wife take over all property paper under there custody. But a few days before my father asked the brother to give it to him, but he refuses to give. He said I would not give it to you at any cost. His wife also threatens my father severely and get back to there home with her brother. After this, my brother also threatens to father and challenge him that you cannot do anything to her. My father always gets afraid, and due to this, he always asks them to sorry every time. My father wants to will his property and wants to give a share to all three children, but younger brother and his wife don't want this at all. My elder sister is also staying with my father with her two daughters and taking care of my father after his paralyzing attack. Brother and his wife didn't take care of him at all. I have some doubts that they have done something with the property because my father said to me that "ye kisi k saath mil kar kuch bhi kar sakte hai." Now I want to know about the property of what they have done with it. As I know, this property is the self-acquired property of my father, and it's GPA based property. Kindly consult what I can do on my father's behalf. I live with my husband and child on rent. We are not much financially secure presently. Please advise. Thanks in advance