Can a sub tenant become tenant

We are the subtenant in the shop in mumbai as our ex tenant has inducted my grandfather in the year 1967 with the concent of ex landlord orally and the tenant used to give rent receipt in my grandfather and father name the ex tenant died in year 1984 and due to lack of knowledge we didn't do anything now in year 1999 the old landlord sold the property to new landlord now new landlord is removing us saying that you are a illegal tenant but we have ample of documents since 1967 till present(2017)- 1)electricity bills 2)income tax documents 3)bmc licenses 4)affidividit for self declaration(1992) 4)rent receipts by ex tenant 5)purchase bills and many more... now the problem is tenant is been dead and his legal hears ran away as they are rich and also not coming in court so is there any law other then section 15A of bombay rent act to give more protection or i can become legal hear of ex tenant as my grandfather and father was there since 1967 also we have done self redevelopment in 2017 after declared delaplated by bmc it costed around 3lakhs for self redevelopment now my right increases as a tenant or not my father died in 2016 and his wife son and daughter are doing business there. and the landlord is not accepting rent since 1999 and also after giving in writing in 2006 he is still not accepting. plzzz help me in solving this issue and also i can became a tenant or not..