Self property

You can give a police report for Extortion and Criminal Intimidation.

You had better gift the property to your younger son rather than executing sale deed.  Stampduty is cheaper in case of former than in case of latter.

Your wife can make a gift in favor of the younger son if she wants but in my opinion executing a will in his favor will be a better option so that the ownership of the property will remain with your wife till she is alive. Your elder son cannot force your wife to register the house in his name. What legal action can be taken against him depends upon the nature of threats given and also whether he is living with you. However, If he is living in that house with you, you can ask him to leave that house and stop him from entering into that house legally.