Hi Skeptical78,
I would like to help you. I have taken a different approach with my family,and I have found success. When speaking with my family members, it has not been my goal to Prove That the Society is Wrong, rather my goal has been to Prove that the Bible Is Right. Gods Word when coupled with Holy Spirit is the most powerful force any human can possess.
You can do all of the research in the world about WT past. You can reel off dates like Wikepedia, You can memorize the Proclaimers Book.. You can have a grasp on every failed prediction & Scandal in History..The problem is if your family does not know what they believe, all of your effort will be waisted.
Many witnesses have no idea what the WT actually teaches! The task of teaching them what the WT teaches now will be almost impossible, since they will have pre determined, anything that you say is from "Apostate Sources"!
If you would like some more advice, please let me know.. I have a few simple & thought provoking questions that you can review with your family. The only source of these is the Bible.