1,924. An Adult and a Minor
Yibum v’Chalitzah 5:30
Let’s say that the deceased’s widows are an adult and a minor. If the yavam is first intimate with the adult and then he or one of the other brothers was intimate with the minor*, it does not invalidate his marriage to the adult, though the minor is instructed to dissolve the marriage through refusal (miun). If he was first intimate with the minor and then he or one of the other brothers is intimate with the adult, the minor is instructed to dissolve the marriage through refusal and the yavam should remain married to the adult. The is because relations with the adult constitute a complete marital bond.
Yibum v’Chalitzah 6:1
Some brothers are fit to perform either yibum or chalitzah, and some brothers are not fit to perform either yibum or chalitzah. The widows are not bound to the latter and are free to marry others. Some brothers are fit to perform only chalitzah but not yibum, and some brothers are fit to perform only yibum but not chalitzah.
*The intention of the halacha is not to recommend such a thing, merely to address the halachic impact should it occur.