Have not been writing for some time, sometimes reading though - wanted to give my 2 ct. because I was asking myself this question, too, about my aging parents who have been JWs all their life.
My conclusion: I decided I don't want to rip their life apart. They built everything on this belief. Every little decision in their whole life. In fact this is their life. If I pulled - or tried to pull - their belief away from under them, they would lose the basis of their life. I can't imagine they would be very happy to realise at this late point in their life, that they believed a lie all their lifetime. How would it make them feel? How would drawing such a balance of their life make them feel? It could possibly even kill them literally, as it would put them in an emotional turmoil that could be fatal as both are having health (heart) problems. Sure, it's also possible they would simply thank me for opening their eyes but honestly I doubt that.
So, to me it's sort of a labour of love to keep my mouth shut and let them believe as they wish. Live and let live, so to speak.
Sure, I don't prospect from such a decision, but they surely do.
I definitely have a different perspective if the person in question is much younger or just about to get into it. Totally different situation. So in the mentioned situation I would give anything I could to make them see the "truth" for what it really is. But as it already has been stated: I would recommend to try to reach all of them.Sort of bombarding the whole family from different sides/people.
Love, Debbie