Tenancy rights Shop

Dear Sir we are based in DELHI. My grandfather had rented a shop on ground floor to a chemist 40 years back through a informal contract at that time. The tenant named Mr S Narula and his son who joined business 10 years back on same shop has been running it. The initial rent receipts were in name of Mr S Narul and around 2003 the rent receipt was made in name of both by my grandfather without any formal contract or change of initial agreement whose copy we dont have. My grandfather passed in 2008 and by WILL the shop was transferred to my father who is paralytic and very old. Father continued to take rent on combine rent receipt name and monthly rent is Rs 300/pm. Few months back Mr S. Narula the original tentant who has entered into agreement with my grandfather has also died and since then his son is running the shop and paying same rent. My father has not entered into any agreement with him and in absence of legal knowledge he has been continuing taking rent since last 6 months from the time Mr S Narula passed away. please advise me since both of the original principles - my grandfather and Mr S Narula is dead , cant this property be free from tenancy rights and cant we current tenant evicted ? since there exist no formal contract between my father and Mr S Narula son so is this shop still under tenancy rights ? and can Mr Narula son continue with the occupation For getting license changed under chemist shop in new name the son of Mr Narula need our NOC and a rent agreement to be given to drug controller. is it possible to use this for getting shop vacated without going into legal battle as my father is bit orthodox for legal batle ill be obliged by your guidance on matter please