There is no wonder pill to open a JW mind. Remember that religion is based on faith; that is, believing in things that can not be proven. People that want to believe something will justify what is obviously wrong to everyone else with thought stopping statements such as "the light gets brighter", "it is not for us to question the ways of Jehovah" and "there is no where better".
That said, it is great you are trying, and there are many JWs that are ready to move on, and need someone like you to guide them in the right direction.
The most powerful thing with the UN is to print off the UN letter, and then tell them that they can look at it on the UN website.
There are a lot of quotes at jwfacts.com that should help. Particularly useful is to ask questions about
- the history of the religion with all the pyramids etc http://jwfacts.com/index_files/davinci.htm
- the current illogical blood stance, print out the chart and ask the listed questions http://jwfacts.com/index_files/blooddoctrine.htm
- who was the Slave prior to Russell http://jwfacts.com/index_files/5min.htm
However I can not stress enough that a JW is brainwashed and will totally dismiss logic. For instance the response I get everytime I ask "why can a JW have a blood fraction if they can not donate blood?" is "it doesnt matter because taking blood fractions is a conscience matter". The answer is irrelevant and totally sidesteps the question, but almost every JW I have asked has said the same thing. The only approach is softly, and only then will work if they are ready to move on. Even if it does not work for now, you will be planting seeds that they will mull over during the years to come.