Sam1, it's good to have you here. You have done exactly what you needed to do to protect your daughter. As the Adult Child of an Alcoholic Mother and severely codependent father, I can tell you have done what I wished anyone would have done for me when I was growing up -- put the well-being of me and my siblings first.
Addiction is powerful, cunning, and baffling, and while your questions are completely understandable, you may not ever get satisfying answers. But if you keep your well-being and the safety of your daughter in your sights you will continue to make healthy decisions despite whatever drama and chaos your wife and her family stir up. I hope you stick around here for support as you navigated the road ahead.