Father gave ancestral property to cousion by emotional blackmailing.

Sir we are four sister and having no brother. My father gave our all ancestral property to our cousin in Aug 2014. He made a release deed. My cousin took fraud signs of my two sister in that deed as a witness. On that day they were in collage. My cousin do this all by emotional blackmailing my father. But now my father has learnt lesson,Sir plz guide us how can we get our property back.