Transfer documentation process

Dear Experts, My maternal uncle purchased a small shop in the year 1995 in Mira Road-Thane district,Maharashtra directly from the builder. The property is not registered as it was not compulsory to register property before 2001.It became compulsory only after the Registration amendment act in 2001.He passed away intestate in 2002 and my aunt in 2007.However the property was in his name until 2015 and later it was transferred in the housing society to his younger son after completing the formalities like Appendix 17,19,NOC affidavit,public notice etc.Out of the two son,the elder son is abroad and he is not interested in any claim from the property and he has no objection if younger son wish to sell property and retain the sale proceeds.Before selling the property what documents are required to claim that he is the sole owner so that transaction is hassle free. Thank you.