Legal heir certificate

I have 4 sisters and one brother. Our parents are no more. My 4 sisters realise their 4/5 share in my favor and that's why I become owner of 5/6 shares and my brother become owner of 1/6 share in a room which comes under Mhada Mumbai. To show relationship and we are the only legal heir Along with registered right release deed we attached our parents death certificates, old ration card copy which is from 1995.on that ration card my father's and mother's names are along with names of all 6 siblings , after my father's death talathi of our village did Varas panchnaama so from 1999 to till today we all 6 siblings having our names on 7/12 of village property, assessment of our village house which has names of all 6 siblings on it. After giving all these documents still Mhada authorities asking for legal heir certificate so my question is..After giving proof of we are the only 6 legal heirs from last 23 years to till today and we have registered right release deed still mhada asking for legal heir certificate is this legal????? Please help me out