It's best to take your time. As others will have told you, your parents are probably so zealous they will swallow the party line from Watchtower corporation hook, line and sinker.
Best be very careful, you can't coerce people to leave the WBT$ unless they want to.
Just ask sincere yet impossible questions from time to time, possibly in 'family study(tm)'.
Don't be blatantly 'apostate(tm)' with them, Watchtower mind control might turn them into not such nice parents.
Beware. Cautious as doves, subtle as serpents, as they say.