Regarding the property issue

Dear Sir/Madam, My problem is that our building is being redeveloped by one of the builder. It takes 12 years to complete, still it's in final process. My home was on my grandfathers name who was died in 1982. After that it is transfer in my father's name in 2007 when building started for redeveloping. Before that our Landlord took notarised NOC of all the members of each residence, for redevelopment, to transfer all the rights in my father's name (who was only residing at this home). In this 12 years, developer giving rent to us. Now question is that my Cousin brother raised the notice after 12 years that he is demanding this 12 years rent + Property share of theirs. Can he get the same? or we can fight further? Because we have the Notarised Consent Letter stating that all brothers & 1 sister of my fathers transfer all the property rights of the said room. Also our tenants list was published in 3 newspapers & also given finally to MHADA as my father is the owner of the said room? Can this be strong evidence in our part?