Builder denies to give my portion even after mentioning my ownership in development agreement.

A lbenami and bought by my father before my birth in the name of my elder brother when he was a minor. Suppose in the name of X grand son of 'Y'. later they gone through a rectification that here grand father is not from parental side is from maternal side. Dada rectified by nana; now in a family gathering my father orally distributed it to my elder brother and to me. we have given it to a builder to development. Since the land was in my brothers name builder did agreement with my brother with consent of me and my father. we are as witness there. perhaps we believe our brother there is included one matter about this. "Mr. X through oral mutual family arrangement, partitioned his share of four flats acquired from the developer as valid consideration of his property. He retained two flats and relinquished his right over two flats in favour of his brother, Shri 'C' and thereafter they will remain in seperate and exclusive possession of their own respective flats." and in later parts of the agreement also mentioned the flat nos and their owner name. Now my brother and builder denies to give my partition mention in development agreement. Builder is telling i will give it to your brother and ask him. and my brother denies it give to me. My questions are what can I do in this case while during agreement it was expected that only four floors could be constructed but they took permission fort five floors and constructed one extra illegal floors. one extra flat also given to my brother. kindly guide me. what to do? also what is rera telling on it? it is rera certified flat with 5 floors.