Redevelopment of tenancy building in suburban mumbai

My cousin is staying in a landlord owned tenancy building since 1971. His single room carpet area is 141 sqft. The landlord has decided with a builder to redevelop his building alongwith with same landlord's adjacent similar tenancy building. In his building all the other tenants are having 1RK area. The developer is offering 20% extra carpet area to all tenants except him. As his area after 20% is 169 sqft, he has offered him to vacate , offering the market price for his area. But he has informed him that he does not want to vacate. Developer replied that he will try to accomodate his 169 sq ft area in the redeveloped building. The rent receipt is in his mother's name who passed away 5 months back in Dec 2018. He has been informed by his friends , well wishers and other tenants that he is eligible for min.. 270 to 300 sqft as per the new dcpr 2034. I require your advice and guidance on the above matter .What is my cousin's eligibility and the legal standing , he being the only tenant with single room.