Conversion from tenancy to ownership

We are 10 tenants in Kolkata which is 65 year old building. Tenants & landlord have agreed for conversion from tenancy to ownership @ Rs.1000 sq feet approx while circle value showing apr Rs. 4500. Huge diff. We had complain to IGR but all in vain. now CA telling once I pay registry as per 4500 and pay cheque to landlord as per 1000 then later I will IT notice which buyers get usually. pls help Arpan Goenka - 9830096144