Goa cancellation

Sir we are staying in bangalore and our ansisteral property is in tamilnadu, my father's is 78 years old he has 2 brothers, one of them stays in Mysore and other in tamilnadu, my uncle from tamilnada use to manage the property,few years back he told us that someone has filed a case on this property, then my father and his younger brother went to native they met him and discussed all the thing and my uncle suggested to get a GPA done on his name as they will not be able to attend the cout hearing and so give the full power To him. Later we came to know that he has sold some portion of the property, My father and his brother reached native and enquired about this then he said he will share the amount among us, but he did not do so he only gave dates and kept postporning, my uncle from Mysore had a sivear hart attack and he passed away, my father in this feeling Became very sick, now he is suffering from Parkinson's and alzemar dises, My question is 1. Can the gpa be cancelled now 2.for cancellation of gpa is both the party requied to be there, that is all the three brothers, 3.what happens to the property which has been sold after the gpa. 4.procedure for cancelling the gpa, 5.as it is a registered gpa how should the gpa be cancelled