Answer: There is no harm in that. A man may marry the daughter of his father’s wife if that daughter is from another husband, as stated in the question, for there is no blood relationship between them—unless a foster-relationship through breastfeeding exists, such as his having been nursed by her mother or her having been nursed by his mother. In that case she is forbidden to him by virtue of fosterage. If no such breastfeeding took place, then no tie exists between them and he may marry her. And Allah knows best.
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Question: A man married a woman who already had a daughter, and Allah granted them children. May the man’s son from another wife marry this daughter of the woman his father married?
Answer: This concerns marrying the daughter of one’s father’s wife when she is from another man. There is nothing wrong with it, for there is no blood relationship between them; she is a stranger to him and he is a stranger to her. Therefore it is permissible for a person to marry the daughter of his father’s wife who was born to another husband.
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Question: A married man with children took a second wife. After some time he divorced her without having children from her. The divorced woman later married another man and bore a daughter. Is this daughter lawful for the first man’s son?
Answer: This is the same ruling as the previous case, which we answered earlier. There is no objection to a person marrying the daughter of his father’s (former) wife when she is from another man, for there is no relationship between them; he is a stranger to her, and she is a stranger to him.