Is it permissible for the son of the brother by fosterage to marry the daughter of his sister by fosterage, who was suckled by his father’s wife?

Your sister's suckling from the man makes him her foster brother, due to the Prophet's (peace be upon him) saying: "What is forbidden by lineage is forbidden by fosterage." As for you and your siblings, you have no relation to the man, and it is permissible for him to marry your daughter, unless your grandmother also nursed him.