Father transferred property to grand mother can we claim share

Dear Sir, My father transferred his property (bought in 1977 )through sale deed to my grandmother(mother's mom) in 1987 and thereafter my grandmother gave POA to my mother to sell the Property in 2000. My mother is the only legal heir. From 1977 till now we are paying property tax, electricity bills etc and we are maintaining the property including collection of rent etc.Now my mother wants to sell the property. Can she do that. I am getting views as get fresh Legal Heirship Certificate (No ration card available ), some are saying get it mutuated ,get a probate of will, legal administation etc..I am confused. What is the way out to sell the Property in shortest time. We have a got a buyer who is asking for copies of documents for legal verification.