What is the ruling on a foster brother (whose mother is the foster mother) marrying his paternal half-sister (born to his father and another wife), and what is the fate of the three children from this marriage?

If the husband suckles milk resulting from sexual intercourse of the wife's father, the wife becomes his sister through suckling. This is known as "fahl's milk" (milk from the male), and marriage with it is prohibited according to the majority of scholars. Based on the opinion of the majority, this marriage is forbidden and invalid and must be annulled. As for the children, they are attributed to their father due to the existence of doubt (shubhah) and the father's belief that the marriage was permissible.