it's a hard one isn't it. my parents have left twice before but gone back. dad was six when his newly seperated mother became a witness, mum was sixteen when both her parents started. (although the smoking issue was a stumbler for her parents who "fell away") now they're in their seventies.when i recently learned some of the scandals i tried to tell them, but they laughed and said it was lies. you
know, they're happy?! (well you have to know the family to fully appreciate that one) i've learned through the years that you can't argue with them. (bites tongue in frustration!) they've got a little circle of jw friends that they socialise with. it would be hard for them to pick up the pieces if they left again now. they don't have much else.
the last time they went back mum had been going to meetings on her own for over a year, dad stayed home watching tv/reading. i think eventually he thought "well if you can't beat em, join em" they were very liberal the first few years back, but the brainwashing has now reinforced their holier than thou behaviour.
i don't know your personal situation but for me just planting a little seed is my strategy. i have books on my bookshelf from when i left. "we found our way out", "Jehovah of the watchtower", and "Kingdom of the cults" unfortunately Ray Franz had not told his story at that time. my folks have stayed in my house while we have been overseas, so would have had a chance to read them. I just got my copy of "crisis of confidence" yesterday, so that one will be displayed in a prominent place.
i like the idea of leaving some society letter print-outs lying around, (i wouldn't put them on the coffee table! but maybe on the top of your "to do pile", that's not pushing it but getting it out there. i can't speak for you, but with my parents, rocking the boat doesn't help, only makes things worse.
hope it goes well for you
best wishes D