How about researching with them the physics needed to create a global flood? Not trolling, serious. The WT still teaches the flood story as fact. They even still teach the water canopy thing as fact! Like shooting fish in a barrel.
I know you want to 'lead them to Christ' or whatever.. So *christian hat on* how about asking them about how they truly feel about all of the obligations involved with being a JW? You could share that you find it a drag sometimes. You could contrast the "gotta get to all the meetings and out in service enough so that god might not kill us" attitude in Jw land. Ask if they feel they have to earn their salvation? Then contrast that with Romans and Ephesians where Paul makes a generous effort to explain that the ransom was sufficient, nothing could be added to it. Nothing they can do can have an effect on whether they benefit from the ransom, whatever that means to you. When was leaving that was a big help. *christian hat off*
Are they involved in any extra curriculars? Would they like to be? Playing sports or something can be a good distraction. Plus the added benefits of more non-Dub friends and some missed meetings for games and practice. If you just drop the bomb on them they might feel lost without something else to focus on.
Your kids will be able to sense the changes in you immediately. Make sure they like the changes they see in dad, be cool dad. Even though you're a Fundie lol