Two [men] who betrothed two sisters, and neither one knows which one he has betrothed, each of them gives two divorces. [If] they died [and] each left a brother, each performs chalitzah with both.  [If] one left one [brother] and the other left two [brothers], the single [brother] performs chalitzah with both; and [of] the two, one performs cha- litzah, and the other [may then] perform yibum. [However, if] they went ahead and married [them], we do not force them to divorce.  [If] each left two [brothers], a brother of one performs chalitzah with one [of the sisters] and a brother of the other performs chalitzah with the other [sister]; [then] the two remaining brothers [may] each perform yibum with the [widow] who received chalitzah from the other's brother. [If] both went ahead and performed chalitzah, the other two may not [both] perform yibum, but one must perform chalitzah, and the other [may then] perform yibum. [However, if] they went ahead and married [them], we do not force them to divorce.