shop tenant has fraudulently taken thumb impression on GPA sale deed

hello sir or madam........one of our shop tenant has fraudulently took the my widow grandmother thumb impression on general power of attorney .special power of attorney along with agreement to sale executed on 1 march 2002 without the consent of other legal heirs of my grandmother...so plz sir help me whether that so called tenant can get true tilttle of ownership?( our suit is already going on in district court of delhi and order has been already passed in our favor by district court judge...... n our socalled tenant has filed a suit in high court can we win the case in high court as well?