Is it permissible for the brother of an infant girl [whose nursing established a foster relationship] to marry the daughters of the wet nurse or the daughters of her children, and if he marries the daughter of the wet nurse's son, is the marriage void, and what should he do?

If a woman breastfeeds a girl, there is no objection for the brother of this girl to marry one of the daughters of the breastfeeding woman, or one of her granddaughters, unless there is another reason for prohibition; because the breastfeeding woman is not a mother to the girl's brother through suckling, and her daughters are not محارم (unmarriageable kin) to him.