Title and possession by inheritance

Hello sir/madam, I am living in, Dibrugarh, Naharkatia, Assam. My case is that my grandmother had three sons n my grandfather expired. My grandmother had three sons. In the year 1971 in february, a plot of land 1bigha was purchased by my grandfather in the name of his elder son and he was separated and his share was alloted to him. In the same year in the month of september, another plot of land was purchased measuring 2 kathas, 15ls. Was purchased by my grandfather in the name of my grandmother and since then her second son and younger son had been living on the said plot of land alongwith their family. That although partition has been done amongst the second and third son and they have poseession on their land since their birth. In the year 1997third son also expired and left behind his widow and two sons who are now in possession. In the year 2006 my grandmother also expired and in the year 2015 her elder son also expired. Now in 2019 the legal heirs of third son applied for mutation of said plot of land in the name of second son and third son of my grandmother by inheritance alongwith all relied documents but now the legal heirs of my grandmothers elder son have made objection to it and claimed title,share and possession in respect of said land. My query is that whether they would be entitled to title, possession and share on the basis of their father? Please suggest me some tips. Thankyou!