Parents being toutured by son via phone calls when already he has been barred from entering house

Parents are being toutured by their only son who is a govt.job Dr by phone calls. Son had a 1st divorce after 6 months of marraige,wherein the court fee was paid by father. Meanwhile he had taken 15lacs personal loan to construct his 3storey hospital on a plot on father's name,also father sold his only house to make money for construction to fulfil his son's dream by all staying in rented house. Son n father both had given cheques to constructor for the same. Amidst this parents got to know about his affair outside with a nurse working in same department. Son did his 2nd marriage against his parents will in mandir. He had kept it a secret till months during which parents said u won't stay here after marriage,also u r barred from property, for which he agreed as he said "if giving parents money will fetch me dis gal,then I agree to move out of house." Non of parents attended wedding which was later again performed from his wife's parents side at their place 2months later. Now after 1.5yr of marriage n with a child of 11month,he suddenly calls father n says to give 25lacs (15+interest) or transfer plot with 2bhk constructed house on his name n give it in writing as he doesn't believe his mother will do same after father is dead. He gave time limit of 1month orelse he'll stop paying his monthly installments which in his thought will b recurred from father's plot n constructed house. That 2bhk was done in place of 3storey plan as it was a full flop show of life as parents had no house to stay then. Also son n his wife both are govt servants with his wife being permanent nurse n son being on contractual basis since 5yrs. How are parents supposed to answer this situation as they had kept them outside the house for same callosals to avoid in future. Should they seek local police help or wait as they had made all terms clear before marriage?