Hi
Your sister in law does not have any valid claim on the property.
Your father in law had rightly transferred the property in the name of your husband probably prior to 1983(as your father in law died in 1983).
Prior to 1994, woman were not entitled to ancestral property.
hence in your case, your sister in law does not have any claim whatsoever.
Also law of limitation will apply in your case.
if at all your sister in law wanted to stake her claim, she should have done it in the year 1983 and she cannot reopen the partition that has happened prior to 1983.
Moreover law favours you and your children as your husband was the owner, cultivator and also in possession of the property since 1983 and subsequently after 2000 , you and your children have succeeded in your own right as legal heirs of the properties of your husband.
Also in accordance to Section 14 of Hindu succession act any property in possession of a woman is her absolute property. In your case, you derived an indirect title prior to 1983 when your husband inherited the property from his father and in the year 2000 when you came in to possession of the property as legal heirs of your husband.
Your sister in law is greedy and has been totally misguided in seeking a claim. she will loose her claim in all the courts in India.
Do not worry.