Alcoholic family members?

My husband and I both had alcohol parents growing up. We promised ourselves we would never get drunk in front of out kids or allow them to be around it. The problem is...my sister in law and her husband are heavy drinkers. They think they are not alcoholics because they function well aka they have good jobs. I've never seen them falling down drunk but they get very moody when they don't drink. They have kids of their own and my brother in law yells and cusses at them all of the time. It's getting to the point I don't want to be around him at all because he is rude to my kids as well. This happens when he doesn't drink! but I believe it is directly related to his alcoholism. If he doesn't have the booze he is impossible to be around. They are at every family function so if we avoid them, we avoid the whole side of my husband's family. don't know what to do??