Pink, I'm so sorry you are having to go through this! It's so awful the destruction alcohol takes on everyone! You asked some important questions:
Do you let him carry on the way he is? I've asked myself that question for nearly the entire 12 years of my marriage to my AH. I've come to understand I can't change him. He has to want to change and want help. You next question is the real one...
What if he never changes? You've got to do some real soul searching and decide what you are prepared to live with. What if he never changes? Are you willing to stay with him forever if he continues drinking?
I only can tell you my experience, which minus the father-in-law and kids sounds like yours. I've stayed for now. I'm not sure what the future holds but I know what I'm doing today. What has been the most beneficial lesson for me is realizing that I'm not in control of him or his drinking. The only person I can change is me.
I wish none of us had to go through this. But maybe you could try Alanon. And keep posting on here and asking questions! The people here have been where you are and are sooo wise!
I'm praying for you and your family! Welcome to SR!
Much love and support! Cheryl