I hope you have a strong attorney. You have a right to your own religious beliefs or non-religious beliefs.
Your ex might try to intimidate you into indoctrinating your children. If they wish to go to the KH, I would take them, sit with them silently, then go out for a nice afternoon in the park and/or to a special meal at home or in a restaurant. If they want to talk about the meeting or JW stuff, just tell them you disagree, why you disagree, and that they have a right to choose for themselves what they believe.
The important thing is how your children feel when they are with you. If they feel you are fighting their father, it will not make for a happy atmosphere. What children remember is how they felt with the people they grew up with. What is between you and your husband should have no effect whatsoever on the children.
Painted Toenail, a poster here, recommended some books for children to teach them critical thinking. They are available from Amazon. They are called Blast of Logic (grades 3-4), Logic Liftoff (grades 4-6) and Orbiting with Logic (grades 5-7). For teenagers, she recommended Critical Thinking by Anita Harnadek. I have not seen these books personally, but I plan to buy them for my great granddaughter when she is old enough.
Do what makes you happy. Help your kids learn to make themselves happy and to think for themselves. Best wishes.