Is it permissible for the eldest son of a woman to marry the younger sister of her nephew, whom the mother breastfed along with her own son, and are they considered siblings?

All of the foster mother's children are permitted to marry their maternal uncles' daughters. They are also permitted to marry her (the foster mother's) daughters, except for the one who was nursed by her, because he has become her son through suckling, and all of her (the foster mother's) children are his siblings through suckling.