What legal steps can I take to recover the share of a property?

I am having two brothers and a father. One is elder and other is younger. My father received an amount upon selling an ancestral property, which is a factory site. He is a partner of the factory. Myself along with my brothers signed on all the sale documents but the money was received by my elder brother and father only. Now they are not giving my due share of amount and giving only some portion of the money received upon sale of land. I have no evidences about receiving money into bank accounts of my father. They also submitted annual returns for the year after sale of property. My lawyer asked to get proofs after serving alegal notice to my father and both the brothers. What proofs I need to gather in order that my lawyer could assist further. Also give clue how to handle this issue so that I can speak to my lawyer.