If a man marries a woman and then divorces her, does her daughter become forbidden to his son? And is the hadith concerning the permissibility or impermissibility of their children marrying each other weak?

The marriage of a man's son to his wife's daughter is permissible, even if the man does not divorce his wife or the daughter. Ibn Qudamah stated in "Al-Mughni" that it is permissible for one of them to marry the other, according to the general consensus of jurists, because there is no lineage or cause between them that necessitates prohibition. However, if the father marries and consummates the marriage with a woman who has an infant daughter from another man, some scholars hold that the daughter becomes forbidden to the man's son through fosterage (radāʿah). There is another opinion that she does not become a foster daughter unless she was nursed after her birth from this husband.