Agreement for registration and stamp duty

My Father was a landowner with a building and 5 tenants. we are 4 brothers and 2 sisters. After my Father passed away we approached builder to develop our property and he made an Development agreement where in it is specified that Builder agrees to give us 5 flats ( 4 for brother and 1 for mother) in exchange of our old property including land. He developed the property and gave us the 5 flats also he gave flats to the tenant and rest he sold. He made an individual agreements with tenants but he did not made any individual agreement with us for our 5 flats. According to builder, Development agreement is enough and he said there is no need for individual agreement for our 5 flats. Now our co-operating housing society and registrar insist that we should have 5 individual agreement and pay stamp duty at current value of the flat. Development agreement was done in 2000 and now after 22 years still conveyance is not done. Is individual agreement for our 5 flats is must ? if yes and builder refuse than what is the remedy ? we do not have any possession letter from the builder. though electricity, water, maintenace, property tax etc are paid by all individuals in thier own names