What is the law that applies to converts with regard to relations with their relatives. As we explained, if one was married while a gentile to his mother or his sister and they converted, we separate them as explained [above]. If he was married to any one of the other forbidden relations and he and his wife converted, they are not forced to separate.
A convert is forbidden to marry his maternal relatives after they convert according to Rabbinic Law. He may, however, marry his paternal relatives. [This applies] even when he certainly knows that these persons are his paternal relatives, for example, twins, in which instance it is clear that the father of one is the father of the other. Nevertheless, our Sages did not enforce a decree with regard to one's paternal relatives.
Accordingly, a convert may marry the wife of his paternal brother, the wife of his father's brother, his father's wife, and his son's wife. [This applies] even if they married his brother, his father, his father's brother, or his son after they converted. Similarly, his mother's paternal sister, his paternal sister, and his daughter who converted are permitted to him. He may not, however, marry his maternal sister, his mother's maternal sister, nor a woman who married his maternal brother after he converted. If, however, a woman married his brother while he was a gentile, she is permitted to him.