Flat Registry

In 2012,we Chakraborty family gave our 5 kathas of land to a promoter who promised to promote a g+3 building and also promised to give 3 flats to our family and a covered garage or shop within 2 years.But according to the promoter due to some obvious reasons that plan is not successfully passed and he decided to promote a normal 3 floored building and to give the said properties to us.According to the agreement among those 3 flats,1 flat of 850 sq.ft and the covered garage is to be given to my father,another one is to be given to my uncle and the third flat is to be given to another uncle and 5 sisters of my father.Now the construction is completed and my father is said to sign the necessary documents.So my questions are 1.Which documents is necessary to be signed by my faher? 2.Some of our neighbours who is handed over his flat recently by his promoter told us that as he is the landowner,he has to sign for the registry work of the other flats of his building.But our promoter is telling that there will be no need for us to sign the registry documents of other flats of our building.So is he telling right or not?