I think it was rude for the new wife to show up (with her son) to someone's house when she knows the owner of the house does not wish her to be there. The step-daughter showed more consideration than I would to someone who was not welcome in my house. The person would not be allowed across the threshold and anyone attempting to usurp my authority on my property would be chastised resoundingly and booted out as well.

As for dad fixing something, yeah, that's gonna work. Only one thing will come of that, he'll lose the relationship he has with his daughter.