For almost 2 decades I stayed in even though I knew about the incorrect prophecies and other incorrect teachings. I spoke to an elder about my doubts and he told me to "wait on Jehovah" to clarify things. He also asked me "where would you go?" So I stayed and even defended the incorrect teachings. I would compare it to being in an abusive relationship. Most people stay because they think things will get better and have nowhere else to go.
It took me a long time to decide all of this was wrong and I wasn't going to put up with it anymore.
Be patient with your family. It takes some faithful JWs years to wake up. You want to give this information in tiny amounts and in a joking way. Make it humorous. You can joke about Rutherford and Beth Sarim, what a silly man poor thing hahaha.