Disputed ancestral property

I am belongs to a Hindu family. We are having a property (agro land) purchased by my great grandfather & legally undivided among the successors, still this date. My great grandfather having two sons, i.e. my grandfather & his elder brother. My grandfather is having two sons i.e. my father and uncle. Just one month before my uncle has sold out his share from this property by release deed to his uncle’s son (my grandfather’s elder brother’s son) without taking any consent from my father or grandfather. Is my uncle having any legal right to do so? If not, then what should we do now?