Whether the court can make the sale of property illegal

Hi Sir/Madam My mother's 2nd brother bought a loan of 1,65,000 from my mother. After failing to give interest it came around 3,65,000 in 2005. So instead of giving money he gave his share of property(house) built by my grandfather.(Mother's father who splited his house into 3 shares one for my mother one for 1st brother one for 2nd brother).2nd brother's two sons were minor at that time.Now they are coming to our house and threatening our lives saying we will kill you if u dont give this house back to us for the same amount(3,65,000) that my father has to give for you. My question is Is it possible if they go to court saying we were minors at that time, so the property sold by my father is not valid. In case if they put case will they succeed on it. My mother didn't threaten his brother to give house. she asked for money only. It was their father's wish to give the house instead of money. Now that property has a value of 15 lakhs, but they are asking it for same 3,65,000.