Cancellation of relinquishment deed

My grandfather register his will in 1980 as per which my father and uncle inherited 50 percent share each in a residential property. My father was made to sign a relinquishment deed in 2015 fraudulently and under undue influence of his siblings who took advantage of his medical condition. in this Relinquishment deed it was mentioned that my grandfather died intestate and my dad's two sisters are relinquishing their right in the said property in favor of my father, my uncle and their sister. My dad is a patient of atypical parkinsons which is a rare brain disease affecting congitive and mental faculties. Can my dad now get the relinquishment deed cancelled from the civil court? Also can the subsequent conveyance deed dated December 2018 also be cancelled by court on account of fraud