A wife’s stepson (husband’s son) is her Mahram due to her marriage to his father. However, this Mahram status does not apply to children from her sister’s husband, as they are unrelated by blood, marriage, or breastfeeding. So, she must observe Hijab in front of them and avoid seclusion.

In Islamic law, the Mahram relationship between a woman and her ex-husband’s father remains intact after divorce. He is in a category defined by Allah in the Quran who are permanently Mahram regardless of marriage continuation.

Your wife’s stepmother is not counted as one of your Mahrams, as there is no blood or foster relationship that would make her a permanent relative. So you may not shake hands with her or be alone with her or travel with her.

Your mother’s cousin is not a Mahram for your mother, let alone for you. It is permissible for him to marry you, as you are not a Mahram for him.

In Islam, a woman cannot serve as a Mahram. Only men, through specific blood, marriage, or breastfeeding ties, qualify as Mahram to uphold Islamic principles of modesty and privacy.