What is the ruling on a father's wife spending on her husband's children, and what is the ruling on the husband's children spending on their father's wife?

A woman is not obligated to spend on her husband's children because she is not their heir, which is a condition for the obligation of financial support. However, if the father is poor and unable to provide for himself, his wealthy children must spend on him and on those he supports, such as a wife and young children. This is because providing for the wife is necessary to keep the father chaste, and providing for the young children is for the sake of upholding kinship ties.