The stern questions in your story may have been the wrong approach and could have been handled differently however the rest of your story caused me some concern. Mormons believe in Jesus as do Jehovah's Witness. There are many who claim to believe in Jesus but don't abide in His teaching. We are given a rather stern warning about "fellowship" with them.
2 John 1:9 Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son. 10 If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed: 11 For he that biddeth him God speed is partaker of his evil deeds.
You mentioned "unity of the Spirit" as needing to be preserved first and I agree. There can be no "unity of the Spirit" with those who do not "abide in the doctrine of Christ". You used Ephesians 4:3 which says: "being diligent to preserve the unity of the Spirit". That would mean unity of the teachings of the same Spirit who teaches the same as Jesus taught. Mormons don't teach what Jesus taught nor do Jehovah's Witness. Jesus didn't teach about praying to people who have died nor elevating Mary over men. Then you made this statement:
>>All believers possess the “unity of the Spirit” as the same Spirit indwells us all...the Holy Spirit, the spirit of Christ.<<
All believers" All what believers? Mormons or Jehovah's Witness aren't listening to the same Spirit. Those who teach something other than what Jesus taught aren't of the same Spirit. There can be no "unity of the Spirit" with someone who teaches something other than what Jesus taught as that wouldn't be the same Spirit. And as John said we would be "participating in his evil deeds" if we even wish him God's speed. It seems to me that it's paramount that we "test the spirits to see whether they are from God" before we think we have "unity of the Spirit".
I don’t disagree with anything you wrote here, but if I had included everything you wrote, that would have lead to 100 other things “needing to be said/addressed” and the post would have been endless.