Property details are wrong in a will obtained by deception

Sir/ madam We are 4 brothers,i am elder one .one day my family members asked my father to share his property among my brothers except to me, so they forced my father to put his thumbprint on a will which is designed by my siblings making one of my brother as benificiary.... and remaing two are witnesses... ( their plan is that in future they want to create a sale deed on that property as if one brother sold that property to remaining other two brothers) .while my brothers are designing that will unknowingly they had included some extra portion of land from our neighbours ... my father was against that will and that type of sharing... my father is uneducated so by decieving him my brothers succeded in keeping his thumbprint over that will ..After 10 yrs of death of my father now they executed their plan. Will is unregistered My question is A) since there is mistake in property schedule is the will valid?please help me how to get my share