Marriage with one’s children, grand-children, great grand-children, etc. is not permissible. Nor is marriage with one’s parents, grand-parents, maternal grand-parents, etc. permissible. Marriage with one’s brothers, uncles and nephews is not permissible. According to the Shari‘ah, a brother is one whose mother and father is the same, or they have one father but two mothers, or one mother but two fathers. They are all brothers. But if the father is different, and the mother is also different; that person will not be a brother. Nikah with him will be valid. Marriage with one’s son-in-law is not permissible. This is irrespective of whether the daughter is already living with him or not. In all cases, nikah with him is haram. A girl’s father passed away. Her mother married another person. However, before the mother could even live with her new husband, she passed away or he divorced her. In such a case, the girl can marry this step-father of hers. However, if the mother lived with him, it will not be permissible for this girl to marry him. Nikah with one’s step-children is not valid. In other words, if a man has several wives, then one of the wives cannot marry the children of the co-wives. This is irrespective of whether she had lived with her husband or not. Nikah with these children is prohibited under all circumstances. It is not permissible for a woman to marry her father-in-law or even the father or grand-father of her father-in-law.