Transfer of share certificate and membership without nomination

I am Shreenath R S reside at dharavi living in SRA building and my father has died on 21st march 2017 without nomination and we have share certificate and property letter of society and now we are seeking for assistance from society to get transfer done on my mother name taking me as nominee. We are 5 siblings, I am younger one and there is no objection from others. My mother want to get me nominee as well as legal heir for this house. but society saying that we will do this work taking amount huge Rs. 15,000/- for society will do transfer related procedures but we want legal help and advise in this matter whether to pay this much amount or to go by legal steps and what way is this would be correct. I have my father death certificate and all required documents. Now the issue is society is pressuring us to pay amount or nothing can be done. My mother and I are in troublesome situation and we have no source of income at this time to pay to society. Kindly help in this regard and let us know what will be the legal action can be taken against this society's action.