Gift deed from mother to daughter

Hi Advocate,

                       My grandmother has two daughters(no sons). My mother is the younger one and 1year back grandmother has gifted an house(in which we all are staying) to my mother in the form of gift deed and it has been registered too at sub-registrar office.

My grandmother is staying with us since 10years in the same house in AndhraPradesh and the other daughter is staying in another place.

My questions are

1) Do my grand-mother have the power to revoke the registered gift deed?

2) Will there be any legeal issues with respect to the property from the other daughter that my grandmother has?

3) Do my mother has the power to sell the house after the demise of my grand-mother?

Your help is very much appreciated.

Thanks.

Regards,

 Srinivas R