"and one of them dies": This tells me (that yibum obtains) only where there are two brothers and one of them dies. Whence do I derive (that yibum obtains) even if they are many and they die (that yibum obtains with the remaining brothers)? From "and if there die … of them." If so, why is it written "one"?
Yibum obtains with the wife of one of them and not with the "wife" of two (see what follows). From here they ruled: If three brothers were married to three unrelated women, and one of them died, and the second made a ma'amar (betrothal of his yevamah by writ or money — short of cohabitation), and he, too, died, then she (the yevamah of the first,) receives chalitzah (yibum release), but not yibum, it being written "and one of them dies" — She who is linked to only one yavam (undergoes yibum), but not she who is linked to two, (as in the above instance, where the woman is linked to the remaining brother by the yibum tie and to the ma'amar brother by the ma'amar tie.)