A. In the absence of Will, If the deceased is a Christian or married under the Special Marriage Act (for inter-religious marriage): Where lineal descendant is present:
1. Widow / widower – 1/3 of the property.
2. Lineal descendants – equally to share 2/3.
3. In the absence of lineal descendant, to all grand children equally
4. In the absence of grandchildren, to great grant children equally,
5. Lineal descendant of a predeceased child or lineal descendant of a predeceased child of a predeceased child if present division is based on equal shares, taking the predeceased child to be alive, and a downward distribution amongst the lineal descendants.
B. In your case, sister in law will have 1/3 share over the Father in law property.