1,944. Wives Who are Sisters and Wives Who are Not

Yibum v’Chalitzah 7:9

Let’s say there were three brothers, two of whom were married to two sisters but each of whom also had another wife. The brothers married to the sisters died so the sisters and the other wives fell to the surviving brother for yibum. If he performs chalitzah with the other wives, the sisters are also relieved of their levirate obligations but if he performs chalitzah with the sisters, the other wives are not relieved of their obligations until they perform chalitzah themselves. This is because chalitzah performed by the sisters is an inferior chalizah and does not relieve another wife of her levirate obligations, as has been discussed.

Yibum v’Chalitzah 7:10

The Rambam opines that this halacha also applies in the case of two yevamos from the same house when one is prohibited to the yavam as a secondary relation or because of a positive or negative commandment. If the yavam performs chalitzah with the prohibited woman, the other widow is not relieved of her levirate bond but if he performs chalitzah with the other woman, the one who is prohibited is relieved of her obligations.