Property dispute

My wifes father and mother got seperated when she was 2 years old and thereafter she was under the care of grandfather and grandmother. When the grandfather was alive, he gave the two brothers of my wifes father their share of land, since they demanded and and my wifes wather didn't get anything because he never asked and also he had the habit of drinking. Before death the grand father told all his children that he has given all of them their shares and the remaining land and the house belongs to his granddaughter since she has no one to take care of her affairs and all of them agreed. But unfortunately he could not execute a Will. After the death of the grand father, my wife's fathers ancestral property has been registered in her name with the consent of grandmother and all her children including her father,2 brothers and 4 sisters. But the 2 brothers who were abroad then had not signed the document. Later the brothers changed the mind and taken a stand that they want their share and the document should be cancelled since they have not signed. One of the 4 sisters who signed the document insisted that she will sign only if she get Rs.50000/-as price for her share,10 cents of land and the amount was paid. Under the influence of the two brothers who have not signed the document,now the sisters who have signed also changed their mind and they have come up with a story that they have signed the document since my wife threatened them that she will commit suicide unless they sign the document.They also claim that they were not aware of the content of the document. Now they also demand that the document should be cancelled. Now I want to know 1)Whether document will get cancelled completely because of the reason that the two brothers have not signed the document? 2)Whether the argument of the sisters of wifes father that they were ignorant of the content of the document and that they were under pressure due to threat from my wife has any legal standing? 3)My wife now claims that she should get the 10cents of land that she bought for Rs.50000/- from one of the sister and also her father should get an equal share as the other two brothers got? Please advice