I had EXACTLY the same experience you did in finding out the Watchtower NGO/ UN connection and like you I was in shock. My entire view of the organization and Bethel came crashing down.
But I wanted to rationalize it and for a while I did.
I recieved from the society their form letter explanation about the UN being like any other government and that they just wanted to use the UN library and media facilities.
But it did not work. I saw the UN being the Watchtowers "Egypt". I felt the brothers responsible were disloyal traitors to Jehovah and could not believe the wts was making excuses for them ( different forms over the years bs) and not disfellowshipping them.
I was in shock and so disappointed. I gave up going to this site for a while.
Eventually I returned and joined this board.
The information I found gave me an ever clearer view of what is behind the wt facade. By this time I had already given up meetings completly.
My only relative who is a jw, stopped speaking to me 2 years ago because I refused to go back to the meetings and he treats me as if I am disfellowshipped.
There is so much interesting information on jwn about the wts and what really goes on behind the scenes.
Continue being careful about what you tell your family.
I really like Quandry's suggestion about asking questions to get your family to think.