One thing you have to keep in mind is that knowledge is often not the motivating factor in one's religious choices. Jesus snapped on the Pharisees because they were not confused. They knew the Scriptures and chose to reject them. JWs are shown the truth. Scriptures that establish Christ as sole leader and mediator, Scripture being complete and able to stand on its own, individual responsibility, personal relationship with God, rejection of human understanding... It's all there. JWs know better than to worship the Society, but they choose to, anyway. They're mentally lazy, militantly ignorant, purposely dense, and perfect candidates for cult mind control, in that they crave glory before men. They seek titles, numbers, and positions. They immerse themselves in Watchtowers and ignore Scripture. They are the ones who shut their ears and turn off their brains when they encounter ideas which identify the GB as mere men. They look right at a Scripture which says one thing and reject it for a ridiculous interpretation by a magazine.
The vast majority of JWs want to be in a cult. As frustrating as it is, you're attempting an intervention on someone who probably doesn't want one. Alcoholics Anonymous understands an alcoholic has to hit "rock bottom" in order to have a "moment of clarity". In a cult, this usually happens when the leaders push someone too far and they snap on an emotional level. Precious few people are brought into cults via intellectual means. An appeal is made to emotion, with "truth" as merely a prop. The Bible is strictly for show and only used when it supports JW doctrine or can be twisted to appear to. Same with "worldly" sources. Something has to happen to snap them out of their self-induced daze. I have personally been turned in to the elders for quoting Scripture, so pointing out where the Bible rejects JW mentality is pointless.
JWs don't care about the truth, the Bible, God, Jesus, you, their children, or themselves. They live and die for the cause. Unless they're "fringe" and have one foot out the door at all times already, there is no possible way you can save them. You can lead a horse to water, but you can't make it drink; and JWs have access to all the water they need, but refuse to drink it. As someone who's had drug-addicted friends, I know it's frustrating to watch someone crash and burn. I know it sucks to want to help them, try to help them, give them everything they need to change their life, but have them reject it for something that will destroy them. Sometimes you just have to let go and realize if everybody could be helped, everybody would be helped.
Probably the best thing you can do is tell them you care about them and when they are ready, you'll be there to help them through the transition. The first step is the hardest and they have to make it themselves.