To know what a landlord's legal son can do if a tenant is claiming that I am an adopted son

My father has a property in bangalore and it was rented to a tenant from past 19 years . Few months back my father had filed a case for possession of the rented property since the tenant was not ready to move out .My father expired last week . The case was in hearing state . Now the tenant claims that I am an adopted son of my father . The history goes like this : I was adopted by my father from his brother (my uncle) 40 years back when I was 8 years old . There was just a religuous ceremony and no legal documents were made . After that I have all my legal id proofs ( Aadhar , Election ID , passport , ration card ) which has my current fathers name . only my 10th marks sheet and birth certificate had my biological fathers name (currently I do not have both ) . The tenant wants to just increase the time line of the case . I want to know what should be my next course of action and what are the other things I can submit to claim that I am not an adopted son . What are the things that the tenant might provide claiming that I am an adopted son