Helping my sister-in-law out with a question posed to her by an atheist co-worker. He started out their conversation by asking who Cain’s wife was.
The following link should assist you in better understanding the Catholic Church’s teaching on who Cain and Seth married. If you have any further questions or concerns that are not answered by these links, please contact Catholic Answers directly.
*]Who were the parents of Cain’s wife?