פירוש על יבמות 11:1

A woman who did not wait 3 full months after she was (last) with her husband and she gave birth and she does not know if the baby is a 9 month baby from the first husband or a 7 month baby from the second husband and the first one was a Cohen and the second was from Israel, this makes a Saffek (doubtful) Cohen. The same would be true for a baby Cohen who was confused with an Israel baby and they grew up, each of these are a Saffek Cohen and we impose on them the strictures of Cohanim and strictures of Israel; They can only marry a woman who is fit to marry a priest and they may not be Metamei from the dead and they can't eat Trumot (priestly tithes) and if he married a divorcee, he must divorce her but he does not get whiplashes for marrying her.

Two Cohanim whos babies got mixed up or the wife of a Cohen who did not wait after her husband (died) 3 months before marrying another Cohen and we don't know if the baby is a 9 month baby from the first husband or a 7 month baby from the second husband, in any case, he is a Cohen and we impose on him the strictures of both fathers; he would be required to be an Onen for all the possible relatives (from both fathers' relatives when they die) and they would be in Onenus for him and he would not be allowed to be Metamei from either of the family members and they would not be allowed to be metamei for him. In which cases do these apply? where the marriage was proper, but if this was through harlotry (or another forbidden relation, but certainly with a Cohen) we silence him from the category of priesthood as we would do if we don't know for certain who is the father (but we are certain that he is a Cohen and not a Halal). What is this case? for example, there are 10 Cohanim out of which one of them and had relations with her (the widow or pnuya); even though he is certainly a priest, such that if he intentionally metameis himself with the dead or marries a divorcee, he would get whiplashes but he would not perform the holy services at the Temple or eat priestly tithings (since he does not know exactly who is his father). [Rama: If she was a penuya (a kosher single girl who is not a harlot by the Torah) who had relations with a Cohen and within 3 months married a different Cohen, the offspring is passul from the priesthood. Although, a Cohen who has carnal relations with a penuya and admits that the child is his son, the child is a Cohen for all things (including Trumot and Avoda) and we are not concerned that perhaps she is giving over her nefesh as a harlot.

A man's wife's daughter and her daughter's daughter and her son's daughter are forbidden to him under Torah law. Specifically his wife's daughter, but the daughter of his anusah [a woman he married after he raped her] is permitted to him after she dies. Rem"a: Even while she is still alive, if he married her under the condition that he cannot divorce her (See the Gemara about marriages regarding an anusah).