What is the ruling on the marriage of the son of "S" to the daughter of "P" after the daughter of "P" was breastfed by one of the children of the second wife, and what is the fate of their children?

It is not permissible for a son to marry his maternal uncle's daughter if it is proven that she was nursed by his grandmother's wife with his grandfather's milk, as she would then become his sister through suckling. The marriage must be annulled immediately if it is confirmed that five sucklings occurred. As for the children, they are attributed to the husband. If there is doubt about the number of sucklings, the marriage is not annulled because the default is that that number has not been reached until it is certain.