Will and legal heirs

Slight correction in the question above:

 

X named her son as successor of her house in a registered will. After X died, son lived in the house but did not transfer the title to his name. Now, Son died without writing any will and the title of the house is still on X's name. Who gets the house? Legal heirs of X or legal heirs of Son?

The property will go in the favor of son's legal heirs , it is true that son had not executed that property in his name but it also true that Mr.X had transferred his property in his name by making his registered will , the will is the evidence of his ownership if it was lost from the son or now not is the possession of sons legal heir then they can obtain it from the registrar office .