Mother's brother took signature on release deed by false impression

My mother signed some court paper which was presented to my mother by her brother as *paper for power of Atorney* Later it was discovered that my mother put her signature on release deed and paper she signed was release deed.Her brother got transfer all her property. But my mother has not signed on deed writer register. Nor any witness comes to court for cross examination. Again stamp paper was purchased by her brother and he put thumb impression on stamp vendor register. Secondaly signature on deed writer was not of my mother .( proved by FSL report) Thirdly out of two witness one is died and we got 2 Fir against him in other cases. 2 nd witness doesnot come for cross examination. HERE is my question on what other point can we challenge release deed. How to go about it ...Pls help