Property despute

Is the property is standing in the name of your grandmother i.e. registered in her name? If yes, as per the given limited facts, the other children of your grandmother can also claim share in the said property.

no matter who bought property in your grandmothers name ,the property registered and in name of your grand mother will go equally to her legal heirs.

the children of grand mothr  have equal right if there is no will, but if there is a will than they  can not fight it, 

The querry is not clear whether GPA was registered or sale deed was executed in favour of grandmother.  By the above I can understand that your father had executed only registered GPA, by which no title will pass to your grand mother.  Moreover, since both the executant and the GPA holders are died, the GPA will become infructuous.  

Thus, the property will again comes to the legal heirs of your father. come with full facts of hte case. 

Since the property is registered in the name of your Grand mother all her legal heirs are entitled to the property in the absence of any specific will.    Who represented her for registration or who has paid for the property is not the criteria.