Both uncle dividing ancestor property and not giving father's share

Hello, I am a . We have an ancestral shop which was run by my uncle (eldest of three brothers) for 30 years. Around 12 years earlier when my father asked for his space of share in the shop, the other two elder brothers handed him Rs.4 Lakhs (value decided 16 Lakhs/4 (their mother + 3 brothers) in parts over 6-12 months. No legal documentation was done but they got it written in a plain paper that the share of mygrandmother & my father was settled. But they did not settle it between themselves. Now they have decided to sell the shop & thinking of distributing it between themselves (two uncles) when the property value is approx Rs. 1.25 Crores. I want to challenge this & make them pay me my share. Request proper guidance in this matter. Thanks in Advance.