We cannot urge you strongly enough to watch the video below, and then go to aomin.org and check out more resources from Dr. James White. To my knowledge, this man has led more people out of cults such as Jehovah's Witnesses because he is careful to study what they believe, talk to them over periods of many visits, share the Gospel with them in truth, and lovingly challenge them to see that the God of the Bible is not the God they believe in.
Another source for help in understanding and challenging Jehovah's Witnesses, so- called, to be consistent with their own teachings and the Bible.
http://www.proofthatgodexists.org/jehovahs-witness/
For more apologetic resources from
Sye Ten Bruggencate, check out the film "How to Answer the Fool".
