Illegal mutation of will

Land in ques measuring 465m2 was inherited by my grandfather in half and his sister in equal shares. After the death of my grandfathers sister we came to know that a unregistered will has been executed after her death and mutation has been done on the name of my uncle i.e. My grandfathers elder son without the knowledge of interested parties. However he managed to get Afiidavit from 2 persons from interested party(total are 5) and behind d back the signature of my grandfathers sisters are in ques and the signaturea taken from 2 persons i.e sons of my grandfather sister are also in ques. And also when the mutation of the will was executed there were no summons send to the legal heirs i.e the 3 sons and two daughters of the grandfathers sister. Kindly assist on this case -will ishand written and unregistered -the persons present during will writing are strangers - is this mutation is legal coz there were no summons / knowledge of the activity - what can be done about the will - AIR will helpon the case - land is un divided in a joint posession - my grand father inherited from his mother (widow) ans his sister also