If things are as uncomfortable as they are, you can have just her tresspassed off of your property with your local law enforcement. That is the only legal way to get her out of your house, but the recourse from your son would probably make things quite uncomfortable for the family.
Your best bet would be to ask the whole family to leave. Tell your son that you don't appreciate what she is doing to you and to your home. Tell him that he and the kids are welcome, but not as long as the wife is around. Maybe he will get the picture that way.
