Lev 18
8 "You must not have sexual relations with your father’s wife; it would dishonor your father."
If the son is NOT to have sexual relations with the mother in law. Then the mother in law is NOT to have sexual relations with him. That is the exact same thing.
Are you really suggesting that it is ok for her to have relations with him but it is not ok for him to have relations with her. No where does 1 Cor 5:1 say anything about rape as you suggest. Although in this state you have to have verbal consent. So in the case where Lot's daughters got him drunk which in this state is considered rape.
Genesis 19:30-38. After the destruction of Sodom and Gomorrah, Lot's daughters got him drunk and had sexual relations with him to preserve their family line. This resulted in the birth of Moab and Ben-Ammi, who became the ancestors of the Moabites and Ammonites.
The descendants, the Moabites and Ammonites, had a complicated relationship with Israel, often opposing them and being seen as outside the covenant community. Their status as "lost or saved" isn't explicitly detailed in terms of individual salvation but rather seen within the broader narrative of conflict and estrangement with Israel
They were not considered to be a witness or the people of God.