Zwert, I don't think it is necessary to believe alcoholism is a disease to work an Alanon program. Alanon is more about those of us who love an alcoholic or addict than the users. It can help with boundary setting and decision making. Of course it isn't for everyone but for some it can be a life saver.
I've heard alcoholism called "a disease of choice.". I like that as it is different from a disease like cancer. Mostly the idea of "disease" is just one way to think about it. You do not need to accept this idea to benefit from programs for people like us.
May you find whatever support you need.