Yevamos 3:9-10

Yevamos 3:9

Let’s say that three brothers were married to three unrelated women and one of them died. Another brother married the widow with money or a document (but did not consummate the marriage) and he died. In such a case, the surviving brother performs chalitzah with both widows and not yibum, as per Deuteronomy 25:5, if “one of them dies….” From this we deduce that the mitzvah applies to a man who is connected to one yevama but not to two yevamos. Rabbi Shimon says that he can perform yibum with one and chalitzah with the other. If two brothers are married to two sisters and one of the brothers died, then the wife of the other brother died, in this case the widow is forever prohibited to the surviving brother because she was once prohibited to him (as a yevama, since she was his wife’s sister).

Yevamos 3:10

If two men betrothed two women (betrothal being more than engagement; it’s actually a stage of marriage) and, when they entered the chuppah (to complete the marriage), they switched the women, each one is liable for violating the prohibition against relations with another man’s wife. If the men were brothers, they are liable for violating the prohibition against relations with a brother’s wife. If the women were sisters, they are liable for violating the prohibition against relations with a wife’s sister. If the women were niddos (menstruants), they are also liable for violating the prohibition against relations with a niddah. After mixing up wives and realizing the error, the couples must separate for three months to ensure that the women aren’t pregnant. If they are minors and not yet able to conceive, there is no need to separate. If the women are the daughters of kohanim, they are disqualified from eating terumah.