Is it permissible for a young man to marry the sister of a man who is his brother through رضاعة (radha'a, i.e., suckling/nursing)?

This marriage is permissible because the suckling of the suitor's brother is limited to him and does not extend to his (other) brother. What is prohibited by suckling is what is prohibited by lineage. The Messenger of Allah, peace and blessings be upon him, said: "What is prohibited by suckling is what is prohibited by lineage." And the brother of a brother by lineage is not forbidden to marry the sister of his brother by lineage. So, it is even more fitting that the sister by suckling should not be forbidden to him.