"Will you promise that the WTBTS will never change a doctrine from this point forward?" They will have to answer a resounding "No, I can't do that" to that question.
Then come back with " Then you are admitting that some of the things you believe, right now "could" be wrong, beliefs that you use to make life and death decisions could in fact be wrong. You could lose your life or the life of your child due to blindly following faulty beliefs"
NJY