Is my father a 50% partner in the business and assets his two sons started 50 years ago?

My grandfather was started business with his two sons (my father & elder brother)before 50 years. Both were done very very hard work with my grand father. My father elder brother is a educated person and my father is a non educated person. So after few year my grand father out of business, and my father elder brother hold all business and doing hard work, because he is able to do all business activites. And my father was also with him but not a very active person. But now my father elder brother is saying, my father is not a real business partner and all groth are done by myself. And he also not accepting a business partner. would you tell me my father is partner or not and his also 50% partner of all business & assest or not.