Is it permissible for the son of a woman who breastfed her niece to marry the younger sister of that girl?

A woman nursing her brother's daughter makes her a full sister (from the mother's side) to all of her children. The state of mahramiyyah (prohibition of marriage) does not extend to the rest of her brothers and sisters, nor to their paternal aunt's children. Therefore, her male children are permitted to marry any of their maternal aunt's daughters they wish.