Registeration of property

Sir i have bought a property from Mr x he left for saudi after giving GPA to his brother Mr y now Mr y is also leaving for saudi and our transaction is not yet completed he says he will give an registerred SPA to me and he will sign a sale deed and leave it with his mother once the transaction is complete his mother will give me sale deed i have to go to subregistrars office and get the property registerred on my name using SPA i want to know can a GPA holder give an SPA and does the registeration done by an SPA given by GPA holder is valid