Another approach you could take is asking your wife or an Elder for explanations on matters (which they cannot explain).
Blood/Blood Fractions (why are some forbidden? some conscience? some recommend by Liason Committee? Isn't Blood, Blood?) Why did their doctrine change? What about the people who died that could have been saved by taking "blood fractions"?
Organ transplants. Once banned as canibalism. Now acceptable. If their doctrine directed by Holy Spirit. Which time was Holy Spirit wrong? What about the people who died that coudl have been saved by a transplant? Does this make WTS bloodguilty?
Sodom & Gommorah flip flops (8 times)
View of United Nations/ Member of United Nations NGO
Claim to be God's prophet (April 1, 1972 WT) / vs. Prophet who lies is condemned (Deut. 18)
False Prophecies:
Claim of End of World (WT Oct 8, 1968 Pg 23)
Young person not enough time to finish school in system (Awake May 22, 1969 Pg 15)
End to come before the end of the 20th Century:
"Shortly, within our twentieth century, the "battle in the day of Jehovah" will begin against the modern antitype of Jerusalem, Christendom." The Nations Shall Know That I Am Jehovah p. 216
"Some of that "generation" could survive until the end of the century. But there are many indications that "the end" is much closer than that!" Watchtower 1984 March 1 pp.18-19
"He was laying a foundation for a work that would be completed in our 20th century". Watchtower 1989 January 1 p.12.
If directed by God's Holy Spirit, why is the Holy Spirit misleading them?
When else did God mislead/lie to his prophet/representative?
Be sincere. Don't jump around. Force them to admit they cannot answer in front of your wife and children.
What if their prophecy for the End being near is wrong again? Why should your kids miss out on a better education/better life?
Tread softly.
Doc