I am the owner of GF and third floor of property and in posession of second floor of property while my sister is the owner of first floor and second floor while in posession of ground floor of the property. Second floor is half constructed so technically I can't construct the third floor of the property. Me and my sister are owner of the property through sale deed executed 26 years back by my mother who was the original alottee of the property, but we never interchanged the posession as we both were not in good talking terms so we never thought of taking the posession of our original floors. Now my sister has sold her share to the third party ( first floor and second floor) and has given the posession of ground floor to the third party while posession of first floor remains with me.
Please advise what are my legal remedies as the third party is not willing to construct the second floor depriving of my rights to construct the third floor and how can I legally challange the sale deed executed 15 days ago between the third party and my sister