Your family sounds a lot like my dad's family. Quick to judge, and to shun. There are whole branches of that family I've never met because they displeased my grandmother once upon a time. Even she doesn't remember why at this point.
It's great that your fiance is so involved with his AA recovery program. Have you checked out any Al Anon meetings? Many of them are held concurrently with an AA meeting. Your family of origin might not ever really "come around," sorry to say. I've been estranged from my alcoholic dad and his family for 20 years. It's kind of a relief, tbh, because I don't have to expose my children to that dysfunction.
But something I've seen in my time in Al Anon is that people in the program tend to form their own family. A couple of weeks ago some friends of mine renewed their vows for their 20th anniversary. They had the ceremony at the Alano Club. There was a band and food and coffee and cake. I brought my gentleman friend and my youngest son. Lots of people had kids and grandkids there, because they knew it would be a family-friendly event. Instead of a ring, the groom's sponsor gave him a special AA medallion that the bride had picked out and designed. It was a really beautiful day.
So yes to all the advice above. Learning about the disease of alcoholism, living your own life as you see fit. But it also sounds like your family has some unhealthy behaviors and dysfunction going on. I didn't start sorting all of that stuff out until I was an adult working my own recovery in the Al Anon program. It helped me a lot.
And I know a lot of people who don't particularly associate alcoholism as the source or cause of the dysfunction in their family but who have benefited from the Al Anon program.