Yevamos 11:5-6

Yevamos 11:5

Let’s say that the son of a kohein’s wife got mixed up with the son of her servant so that they didn’t know whose is whose. Both boys may eat terumah and they split a portion from the threshing floor, neither may become impure for a corpse, and they cannot marry because kohanim may only marry women who are fit to marry kohanim and servants may only marry women who are unfit to marry kohanim. If they grow up and free one another (so that whoever the servant is, he is now free), they may both marry women who are fit to marry kohanim and they may not become impure for a corpse, but if they do, they do not receive lashes. They may not eat terumah (because one of them is a freed slave, no longer entitled to terumah) but if they do eat it, they need not repay it and pay an extra fifth. They do not receive a share from the threshing floor. They may sell terumah to kohanim and keep the money. They do not receive sanctified items from the Temple; they don’t offer sacrifices; they may give their own offerings to any kohein they choose; they need not give the portions of shoulder, cheeks and abomasum; their first-born animals graze until they develop a blemish; they must follow the stringencies of both a kohein and a Yisroel.

Yevamos 11:6

Let’s say that a woman did not wait three months after being divorced or widowed before remarrying, then she had a baby and it’s unclear whether it was a nine-month pregnancy from her first husband or a seven-month pregnancy from her second husband. If she had other sons from each husband, they perform chalitzah and not yibum. Similarly, if one of her sons whose father is known dies, this son whose father is unknown only performs chalitzah, not yibum. If he had brothers from each of his potential fathers but they had different mothers (so that some are half-brothers and some are not really brothers at all), he may perform yibum or chalitzah for them and, for him, one performs chalitzah and the other may perform yibum.