Frauded by Uncle regarding Sale of a Shared Family Land (EJMALI Property)

Dear Sir Brief of our family Our family (Roy Bari) an ancestral property at Krishnagar Nadia, My Grand Father are 4 Brother, Brother one had One Son, Brother Two had 3 son, my grand father was the 3rd brother, he had two sons (My Father (Having 2 Sons Me and My elder Brother) and My Younger Uncle (No Children)), and Brother Four has 4 Sons. Currently Except us i.e. My Father and My Uncle, everyone sold off their property years back, Now After demise of my father in years 2014, We are left alone (Our Mother, My Elder Brother and ME) with our Uncle (from father side and his wife) Coming to the Case. As we are in Krishnanagar for almost 250 Years, our family has some Shared lands within the property since inception i.e. Small lanes within the primises, few gardens etc., as time passed away many of these Shared lands are sold after having written consent from all family members. Now only two of the shared land left before the year 2014. But in the year Feb 2018, all of a sudden my uncle (from father Side) along with Another Uncle from (4th Grandfather Side) jointly sold off one of the remaining land, for the same we have not given any written consent, as far as we came to know from anonymous sources that these two uncle had sold the property by saying they have POA in their name. This year we suddenly came to know about the fact as for more than 25 years we live in Kolkata due to my father’s service. Now kindly suggest what action we should take to safeguard the property which was sold fraudly, and how we can get the sale deed from govt, Eagerly Awaiting for your reply.