Co ownership

My grandmother and father are on deed together. My father has been inhabiting the property for over 20 years. My grandmother was added to the deed at the same time as my father, about ten years ago. My uncle now has power of attorney for my grandmother. My father wants to sell the property. My grandmother hasn't ever paid any of the taxes, made any improvements or lived on the property. How does he go about having her removed from the deed? Does she need to be bought out after the sale? Could he legally buy her share from her and then sell the property? If he buys her out after the sale, could he deduct half of the taxes he has paid on the property since she was added to the deed? Half of provable improvements? Is there a way to have her removed if her half of the taxes owed equal more than half of the property's value? Any information on this complicated matter would be helpful.