Will a married man remain in a marital relationship with his wife if her daughter is breastfed by the wife's mother, and what are the resulting rulings?

The suckling of a girl by her maternal grandmother does not affect the marital relationship between the parents. Rather, the prohibition (of marriage) extends to the maharim (unmarriageable kin) of the wet-nurse, whether by blood or by suckling. Thus, the wet-nursing grandmother becomes a mother to the girl (by suckling), and the (biological) mother becomes her sister by suckling, and the sons and daughters of the grandmother become her maternal uncles and aunts (by suckling).