Query Regarding Partition Of Willed Property Without One Of The Beneficiaries

My late maternal grandparents had left a will ( in 1985) before their death by which a particular property was to be divided in the manner: a portion of the property to my Mother & balance of the property among one child of my elder uncle & two children of my younger uncle. Now one child of younger uncle married someone belonging to another religion (without will or knowledge of uncle & is in-communicado with the family). Now rest of the legal beneficiaries (my mother & 02 cousins) are unable to get the same partioned due to our unwillingness to contact her or even bring up the issue with uncle 73+ years old). What is the legal option available with us.