Probate/Will case

Hi Sir, My story begins with my father they are three brother, Lets assume big brother as A, Second as B and 3rd one is C. All they are living in combined family, C is working as a teacher( My Father) and only the person who can earn in family, but as per tradition A is the whole sole owner of the family. Now they have buy 10acre of land on the named of A in 1960's. and 8 acare they had with my grand father ie: total 18 acare of land. A don't have child nor wife. B has 6 son's And C has one child ie:me. A has stared the selling the land as he was sole owner of family,so that we had separated. before the separation he had sales 3 acare of land which they had brought earlier, because of combined family all the 10 acare on his ( A) name. so we had separated with (18-3)/3 = 5 acare per head. After the separation all the land's mutation had been done and B and C are paying all his owned land taxes, on that separation he mentioned that on paper and accept that i had sold the land which we have buy combine , but i am the whole sole owner of family that's why all the lands on my name. After the separation he (A) had also sold 3 acare more. After his death all the Family member of B and C had did his funeral. and the rest of his property has divided into among of us ie: (5-3)/2=1 acare /head. and all the share divide had been happen on the Panchayati. based on this panchnama we all have doing the agriculture and paying the land tax and Rasheed and also name on register-2. After 15 Year of these things one of them member who sold all of his land and claiming the Will that "A" had written a will for all his own land on his name should be transfer to Devi B son's of son's after his death. While during the panchayati he had not present any kind of the document and also signed the punchnamna, the Will document which he is showing is not registered in Court, But the will document which he is showing having the judicial stamp of 100 rs and signature of A .we dont know what is the purity of the that will. SO my query is as per the situation is that his Will would be vaild as we all are paying the land tax and already having the name on Register-II. As per the calculation if we can calculate the total land of ie (Buy+previously owned)=18 acare. if we can divide into the three part that should be 6 acre each. But As per the above things you can see A has already sold 6 acre , 3 acre previously separation and 3 acre after separation, so is that logic would be valid for voiding NULL of the WILL. But important part is that all the land which they had buy by combined family are on the Name of A. Please suggest what to do in the case , hope for your earliest reply.