Landlord vs Tenant: Building need to repair there is external major work outside portion

Dear Madam/Sir, Am Tenant of Bldg premises from last 30 years in gaothan. The landlord is deceased & there are 9 children of owner (6 Daughter/ 03 Son). Now we are paying rent to his elder son more than standard rent. Now BMC has issued us notice to conduct structural audit of bldg bcz more than 30 years old. owner did not reply to notice. where BMC issued other notice of unauthorized construction instructed us to submit proof evidence of bldg we submitted the Sanad copy & Assessment, electricity copies prior to 1990. Now we have conducted audit now contractor had given us quotation for repair where we need to contribute 2 lac each against the external (major) repair. But what i understand its landlord duty to keep bldg in good condition. Even landlord charging 600/- Rs monthly from us without any receipt My question is What will be ratio or percentage to contribute for external repair work which need to be carried ? What benefit or relief shall we demand from landlord (levy on rent)? or can we ask him to give us ownership of room ? Please help me out