דיני צרת היבמה וקרובותיה ובו ה"ס:
הכונס את יבמתו נאסרו צרותיה עליו ועל שאר האחים בעשה:
When a man performs chalitza (ceremony to undo the levirate bond) on a woman bound to him for levirate marriage, that woman and her co-wives become forbidden to him and to all his brothers by positive commandment.
A man granting chalitza (separation ceremony for a woman bound for levirate marriage) to his [late] brother's wife, is Rabbinically forbidden to marry her relatives, even second degree relatives. Similarly, she is forbidden to his relatives. But his brothers are permitted to her relatives. Note: Even if he performed chalitza out of doubt, he is still forbidden to all her relatives (Mordechai, beginning of chapter haCholetz).
A man is permitted to marry the sister or other relatives of the co-wife (tzara) to his [late] brother's wife to whom he had given chalitza.
If is forbidden to marry the co-wife of any of the relatives to his [late] brother's wife to whom he had given chalitza.