Study Yevamot folio 23B with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
Mishnah: In the case of one who betrothed one of two sisters and does not know which of them he betrothed, so that both are forbidden to him, he gives a bill of divorce to this one and a bill of divorce to that one due to the uncertainty. If the man who had betrothed one of these women died before
If the man who betrothed one of these women had two brothers, one of them performs ḥalitza with one of the sisters, but he may not enter into levirate marriage with her due to the possibility that she is the sister of a woman with whom he has a levirate bond. And one takes the other in levirate marr
Furthermore, in the case of two unrelated men who betrothed two sisters: If this one does not know which sister he betrothed and that one does not know which sister he betrothed, this one gives two bills of divorce, one to each of the women, and that one gives two bills of divorce. If the two men
If this one had one brother and that one had two brothers, the single brother performs ḥalitza with both of them, and of the two brothers, one performs ḥalitza and one performs levirate marriage if he so desires. If they married the sisters before consulting the court, the court does not remove them
If the two brothers performed ḥalitza with both wives before consulting the court, the two brothers of the second man may not takeeither sister in levirate marriage lest one marry the sister of a woman with whom he had a levirate bond. Rather, one performs ḥalitza and one performs levirate marriage