Devolvement of property after parents death

My father in law (Hindu) constructed a house on a piece of land in the late eighties. He had a wife & 2 daughters. The elder daughter got married in 1992 and has a son & husband. The younger daughter got married in 2003. Father in law expired in 1997 leaving behind a widow, married daughter, son in law, grandson,& unmarried daughter. Mother in law expired in 1998, intestate and the property devolved upon the 2 daughters being Class I heirs. to the exclusion of the grandson as he was a minor. The younger daughter who got married in 2003 expired in 2017 (intestate) and has left behind her husband as she did not have children. The surviving daughter is now in exclusive possession of her parents property. The husband of the deceased is trying to lay claim on the property by foul means and wants my wife to sell off the property. He is a not a Class I Heir and is not entitled to any share but my son is. What is the legal recourse I should take to protect the interest of my wife and son.