A. How did you come to a conclusion regarding the nature of property is ancestral?
B. Which types of agreement were executed from your grandfather?
C. In case, property is ancestral, your grandfather cannot execute any agreement in favor of you. All class I legal heirs i.e, 6 kids will get an equal share over the property. However, in case, property is self acquired property, then only your grandfather can execute an agreement in favor of you.
D. Therefore, in the absence of a Will (died intestate), first, all legal 6 legal heirs will get an equal share. Subsequently, your father can enjoy the property till his lifetime subject to property is self acquired or inherited from your grandfather.