Father in Law wants to move in for Summers. Am I wrong to be opposed to this?

Considering your past experiences with them, I would have to agree with you 100%. You are the man of the house... Put your foot down. You need to explain to your wife, and she knows it, that because of past experiences with her mom and dad, you cannot ALLOW them to stay at your house. Explain it to her very honestly. And tell her that it may ruin your marriage, and that is why you won't ALLOW it. Tell her that you will let her inform her parents, but, if she can't handle it, that you are more than willing to make enemies with them over it, and that you will have to talk to them yourself. Tell her to pull up her big girl panties and handle her family.