Is my wife's father considered a forbidden (mahram) relative to me after his marriage to another woman? Is it permissible to shake her hand, look at her hair, and kiss her head, as some scholars have ruled?

If a man marries a woman, the wife's ascendants (mother and grandmothers from both sides) become forbidden to him, as Allah the Almighty says: "and your wives' mothers." However, the wife of the wife's father or the wife of her grandfather, if she is not the wife's mother or grandmother, is not forbidden to him and does not fall under the ruling of "and your wives' mothers." It is permissible to marry both a woman and her father's wife at the same time. The fact that this woman is not a mahram does not mean she should be shunned. Rather, it is permissible to greet and converse with her, provided there is hijab, no khalwa (private seclusion), and no handshaking. If she is elderly, it is permissible for her to uncover her face. What occurred previously incurs no sin if it was based on a fatwa.