Procedure in case unregistered ancestral property issue among brothers

My father has 3 son 2 daughter. 40-50 year ago we bought a home from someone else without any written document.and we have 2 agriculture land without any doc.these lands were gifted by my maternal grand father to my monther. and these land and house are registered against some third person who is living abroad for long time. My mother is passed away recently. my father is blind and he stay with younger brother. now my both brother are denying to share equal part of the property.they have refused to give any single bit from the property.my father is also not supporting me. Now none of the property is registered with my mother or father ,and there is no property will. so i have 2 question 1- does my father have legal right to refuse to give property to me even there is no deed/documents for these property which is registered to 3rd person. 2- Please suggest what should we do in this case ??if we file a case in court how much our case will be strong?