How to change father's name(not spelling mistake)?

Dear Lawyers, My name is Murugan (65 years old), my father name is Rajan and My father's brother name is Ganapathi. The issue here is, all my record shows Murugan s/o Ganapathu where it supposed to be s/o Rajan. Since my father's brother put admission in school, at that time they asked my name and who came along with me which is my fathers brother for admission. That is the way all my records carried Murugan s/o Ganapathi instead of Murugan s/o Rajan. With above record i served govt job and reteried and now gettinh pension as well. My father(Rajan) had expired and trying to get legal heir certificate along with my sibling but we couldn't succeed as my record shows s/o Ganapathi. My father brother had expired long time back and their family got legal heir certificate where my name was not there and my father also expired... How to get it added my father's name in my record instead of my father's brother name? My mother is 80years old and she lost her visiblity and hardly she could listen voice. Since my sibling came to this legal issue..they trying to cheat me in the way without adding my name in legal heir certificate and seperate the land among themselves. How to correct my father name officially ? What are difficulties do i have? I do agree this could have corrected when my father was alive but fingers crossed.