Property as a gift

Dear All,

Need Suggestion on following issue, kindly provide your views.

My Grandmothers Father had 2 acre land in Bangalore, Which he gifted this land to my grandmother, during registration process he clearly mentioned in the deed that gifted property can not be transferred (sale) to anybody by any kind of transaction (Registration or GPA).

However my Grandmother did GPA transaction of this property to other person, person who bought this property through GPA sold to other individuals through Registration process without taking approval or signature from my grandmother. 

Need suggestion from forum members that transaction done by my grandmother is it valid? Can we claim this property back?

Please help me with your views.

P S: In RTC record we are still getting my grand mothers name as a owner of this property.

Thanks