Dear Peter:
I'm not a therapist or an addiction counselor. I am someone who started recovery, decades back in my early 20's.
I'm not sure of the reasons for not sharing with the family for these individuals. Maybe shame or secrecy or the addiction itself or maybe the family is toxic or dangerous, or recovery might mean facing an abuse history and having family relationships strained or ended.
I know there are lots of mixed reviews of the effectiveness, long-term, of 12 step programs, but they are a place to start, anonymously and for free and where there are people of all ages and stages of recovery. And, depending on what the issues are there are a whole lot of options besides AA/NA.
They may be able to support each other and get to meetings together or come up with ideas for what would help them. However, finding a larger support that exists even if one of them relapse, etc. would probably be good. I recommend yoga or other things that help regulate moods/symptoms and there are starting to be ones geared specifically for different groups and they can be a lot more affordable than traditional treatment programs. Cissy