What is the ruling on a man marrying his son's wife out of ignorance, and does that affect the son's marriage, or is the contract void in the first place?

The son's wife is permanently forbidden to the man (father) the moment the son contracts marriage with her. If the father contracts marriage with her, the contract is null and void and does not affect the son's marriage. However, if the father has sexual intercourse with his son's wife, some jurists say that this dissolves the marriage between the son and his wife, while others say it has no effect on the son's marriage. As long as the man has not consummated the marriage with his son's wife, it has no effect on his son's marriage according to any of the scholars.