Or maybe his family will turn on you and accuse you of lying.
Not trying to be the bringer of bad news here, but it is possible. I've seen it on this board before: the spouse of an alcoholic turns to the alcoholic's family and friends for support, only to find them in deep denial OR to find that they blame the spouse for the addiction.
It can be very tricky to involve the family of our alcoholic into the mix. Not everyone is ready to face the music; some will never be.
If you are able to talk to them with no other goal than to impart some information, knowing full well that it may cause a sh*tstorm, and having no expectations of those to whom your impart that information, then by all means go ahead.
IMO, your means of support needs to lie elsewhere, namely in Al-Anon, counselling and SR. If by some chance, your AH's family supports you in your efforts, GREAT; if not, well, it was to be expected.