That IS a hard question. I don't know. You don't want to concede victory to a cult, and yet...you can't beat them. Fair enough. Then you can either set as many fires as possible along the way to promote the real truth about them, or you can walk away. The hurt doesn't go away, especially when you see the literature all the time, hear the meetings on speaker phone in your home, hear them talk about what Sister So-and-so said or did.
People waste their lives on foolish causes every second of the day. It hurts more knowing it's someone you hold dear. But you can't interfere. They have to follow their own path; they have a right to that, even if that path is a fool's errand. If this is the only life we have, being born itself is a fool's errand, too, one we've no control over.
It's reality. You can't change people. Just be good to 'em and watch over them. You can't go wrong that way. The pain is a part of this--knowing it's a cult, that scar never heals, that pain never goes away.