Ancestral property sold without consent of other parteners

Respected sir, due to sudden demise of my grandfather, our ancestral property is distributed in two names i.e. my father and uncle though they have two sisters their name does not appear on the SaatBara. In 2000, my uncle sold 11 Guntha of agriculture land to x person of our village. The sold land is in our possession since the verbal divide of our family and the buyer is having possession of another part of our land and that is to excess. My uncle passed away in Jan 2012. After his demise, his wife, my aunty told me and my father that they (buyer) had cheated his husband i.e. my uncle and without proper sale deed and signature of her, my father and their sisters they have done that transfer. But due to oversight and hurry they have done sale deed of the x place and now holding the possession of y place and that too excess. Can my father, his sisters and my aunty prove this case as fraud because my uncle was heavy drinker, the witnesses who signed on the sale deed are not sure about the clear possession of my uncle of the salling land and buyer buy that land with wrong procedure?