How can my get my share in ancestral property

1.My father has forged our signatures in a simple mortgage deed registered where he mortgaged ancestral agricultural land and got loan from a govt institution in 1994. 2.In 2003 he forced us to sign papers to sell part of the ancestral home to pay for the loan. 3.My father has a brother who died leaving behind a legally first wife and a son through her and a second wife and a daughter and a son through her. 4.Our father, me, my two own brothers, my father's elder brother's first wife and her son have all signed the sale deed. Backyards of two portions were sold. All of our names appearing on encumberence certificate against both backyard details. However the loan was not paid. 5.He used the money to release the rights of my father's elder brother's first wife's son on a portion of the house in 2004 and got in his name. 6.In 2010 he paid the loan got a release deed for mortgaged agricultural land from govt institution. 7.In 2011 my father and his brother's first wife's son sold the agriculture land ( that was mortgaged to govt institution) without me and my two brothers signatures. 8.My father also has two sons from another wife who were born in 1989 and 1992. My mother got divorce in 2006. 9. My father says we three sons from first wife have no rights. 10. Says that portion he got released from his brother's son is solely his. What are our rights and our share.