Builder distress

My father is the landlord and entered in to an agreement with the builder in 2002. Here are the issues: - He took more than 10 yrs to complete the building and gave possession without proper OC (now we have received a notice from the Building proposal department of MCGM to vacate as we do not have an OC)- What action can we take? - He has still not done the registration of our flat. He fears we will take legal recourse on other matters and has delayed it for 10 yrs by talking sweetly with my parents. Can we take any action? - He has not completed the building, have not installed all the lifts, all the raw materials is lying around as he plans to construct 2 more floors - He himself lives on 7th floor that is not a part of the approved plan- we had notified BMC about this illegal construction and also asked them not to appove further construction - He kept us- the landlord on the side and bought flats from tenants and sold it to new buyers during this period. Can we take any action? - He has not paid us the last installment of the decided payment, there was a tenure or the conveyance clause (which ever comes earlier) to pay us the final installment and it has expired long back. Can we take any action? Please assist.