Father's name different in my certificates and to his properties

Dear Sir / Madam, My father's name is Venkataramana and he is more familiar with people by his nick name Srinivasulu. At some point he started using Srinivasulu as his name (20 years ago) thus all his official documents state as Srinivasulu. This applies to my mother's documents as well (W/o Srinivasulu). In the same line, properties registered / owned by my parents are also with their current new names. However my certificates and all other documents refer him as Venkataramana. I would like to know how can I demonstrate in future that I that I am their legal hair on paper? The identity documents (ration card) submitted during registration indicate my name under family members (I am the only son). On my request for a different purpose, my father has got a notarized affidavit stating both the names belongs to him. I suggested him to change his name officially to Venkataramana with an usual procedure according to the G.O. (P) No. 819. 1. Once he change his name officially, how easy is it to change it in the property documents? 2. Is there another simple procedure other than changing his name to demonstrate that I am their legal hair. Is that affidavit sufficient for that purpose? 3. Besides property etc, which is of least interest, I wanted to have clear documents within the family. Any suggestions would be of great help. Thank you in advance Prakash