Delay in registration of property for many 3 years and threatening for money by one of the parties

Sir , the property had been divided among four siblings of my father wherein, upon the demise of my father's elder brother, his son has been transferred his share of property making him one of the parties as mentioned in the registration procedures.Upon the demise of my uncle, his son has been harassing my father for money following by physical threats, though verbal, he has even threatened the promoter involved in the registration process and has not signed the Developer agreement which has delayed in the total process of registration and we are under the anticipation he might not do so under he receives money from my father though extortion.He has even put a lock on my father's shop barring him to enter until my my father pays him.I would be highly obliged in case advice is rendered on how we can prepare legal documents stating we are not bound to pay him any amount of money after the registration process and any kind of physical or mental harassment made to my father by my cousin(my father's elder brother's son) can give us liberty to file a strong case against him.