158 Yevamot 11/4-6

(4) When the son of a woman has become interchanged with that of her daughter-in-law [and each of them has another son, or sons, besides], which sons grew up, married, and died [without issue], then the other sons of the widowed daughter-in-law shall receive Chalitzah [from one widow] but may not marry her by Yeboom, because it is doubtful whether she was his brother's wife or that of his father's brother; but the sons of the grandmother may either marry her by yibum, or receive Chalitzah, because the doubt in this case is only whether she was wife of his brother, or of his brother's son; but if the sons whose descent is undoubted die, then those of doubtful descent who were interchanged, must have the ceremony of Chalitzah performed to them by the widow of the grandmother's son, but may not marry her by Yeboom, because it is doubtful whether she is the brother's wife or that of his father's brother, the widowed daughter-in-law need only perform the ceremony of Chalitzah to one of those who were interchanged, and may then marry the other by yibum.

(5) When the son of a woman married to a priest, was interchanged with that of her bondwoman, both [sons] may eat of the heave, but when both happen to present themselves at the same time at the threshing-floor, they shall receive but one share of the heave; they may not defile themselves with a dead body, and may not marry women who are either qualified or disqualified to be married to a priest. But when they have attained their majority, and have mutually manumitted each other, they may marry the women only who are qualified to be married to the priesthood, and may not defile themselves with a dead body; but if they did so, the forty stripes are not to be inflicted on them. They may not eat heave, but if they did eat it, they need not pay back the principal [of the value they had eaten], and an additional fifth, nor has either of them a share [in the division of heave among the priests] at the threshing-floor, but they are allowed to sell their own heave, and keep the money themselves. They have no share of the consecrated things of the Temple; consecrated things are not given to them, nor are these consecrated things exacted from them. They are, moreover, not bound to give the shoulder, the two cheeks, and maw of their own offering to the priests. Their first-born cattle must be left to pasture, till they contract a legal blemish, and with respect to their sacrifices, the most stringent regulations in force in respect to that of priest and Israelites, are to be applied to them.

(6) If a woman who did not wait three months [to re-marry] since the death of her husband [or since her divorce], should marry within that time, and has a son born unto her of whom it is doubtful whether he was a nine months’ child by the first husband, or a seven months’ child by the second; if she had other sons by the first and second husbands, then these sons must, in case of the decease [without issue] of their brother, to whose birth doubt attached, receive Chalitzah from his widow, but may not marry her by yibum; and he also may only receive Chalitzah from any of his brother's widows, but may not marry them by Yeboom; but if he had half-brothers, either of her first or second husband, who are not sons of his mother, he may in that case either receive Chalitzah of his brother's widow, or may marry her by yibum. In respect to his brothers, one of them must [in case of his death without issue] receive Chalitzah from his widow, and then may another brother marry her by yibum.