Let's put it this way. Every man deserves the woman he has. In this case, the husband is a slacker. The wife brought the fucker and instead of immediately kicking the wife and lover out of the house, he just said a few phrases of objection that had no weight among those two. An even greater humiliation was when, after his wife had been fucked, they took and splattered cum on the husband's face and he again bitch-slapped.
Lady looks like a long time unsatisfied walks, if so easily with her son and daughter was able to go to such sexual intercourse, while she herself has inclined them to it. The son was not confused, noticing through the keyhole what the mother and sister were doing, decided not to lose the opportunity and joined in. Especially since he had previously looked at family photos and became aroused. It was a sin not to take advantage of the depravity of his family.
That's quite a spanking. I think the girl liked that punishment and would do it again.