abacabb3, I'm sorry that your JWs have stopped coming around. Recently mine did as well after nearly a year of regular meeting. Ultimately we should both praise and thank the Lord for giving us the opportunity to share the gospel with them. And we need to keep regularly praying for them. Often they don't respond right away. Some take years to start examining what they have been shown from the Scriptures. And some will respond later when other Christians also witness to them. Many will simply harden their hearts and carry on in unbelief.
For any who may be confused or unaware:
JWs and Mormons are most definitely not Christians. They subscribe to the brainwashing of very manipulative cults that teach a works-based salvation. They may claim grace, but if you really dig into what they mean by the word, you will find it's not what Scripture teaches. The same goes for many other words and phrases they use, like ransom, atonement, lord, salvation, etc. Don't be fooled! These people are caught in lies and deception and are headed for eternal torment in hell if they do not turn to the real Christ.
A few differences to be aware of. These are things that they don't tend to bring up when first entering into conversation with you:
Mormons believe that all souls are eternally preexisting spirits waiting for a human body. They are extremely polytheistic, believing that all men have the potential to become gods just like Jehovah (Jesus) and Elohim (God the Father), ruling over their own planets and populating them with their wives. They believe that Elohim populated earth with his many wives and had sex with his spirit child Mary in order to have Jesus. Jesus and Satan are spirit brothers. No one really goes to hell, but instead a variety of levels of heaven depending on whether they are Mormons, good Mormons, good people, bad people, etc. They believe the Bible is correct only so far as their other books (Book of Mormon, Pearl of Great Price, etc.) interpret it. There are many other differences, but those are a few that should convince you they do not believe in the true Jesus of Scripture. They also don't consider us to actually be Christians and may admit this if you press them on it. They consider anyone who subscribes to orthodox historic Christian doctrine to be apostate.
Jehovahs Witnesses believe that Jesus is really the archangel Michael, and not God. Like the Mormons, they reject the Trinity and consider the doctrine to be heretical and pagan. They believe hell is only for Satan and demons, and that unbelieving people only cease to exist when they die. They also believe that even good JWs can lose their salvation in the next life, which is only a "paradise on earth". They believe that only a literal 144,000 JWs (most of whom are already dead now) can be be born again and see heaven. They themselves, though they like to talk a lot about the kingdom, do not believe they will personally ever see it. The JW religion was developed by a man who grew up in a Presbyterian church and eventually rejected it because he despised both the idea of hell and of election. He was heavily influenced by some Seventh Day Adventists that he came into contact with, particularly because of their focus on prophesies. They also don't consider us to actually be Christians and may admit this if you press them on it. They consider anyone who subscribes to orthodox historic Christian doctrine to be apostate.
Both the JW and Mormon cults have a long history of fanatical false prophesies, which they prefer not to focus on because they are an embarrassment. In the past decade or so, both have started teaching their followers a more "seeker friendly", "watered down" kind of religion so that it's easier to sell and believe. Mormons in particular these days don't seem to know a whole lot about their religion's history or the finer points of their own doctrine. So it's important to be sensitive to this and not just throw it in their faces, but instead gently show them the differences.
For anyone who would like to know more details about the differences between their doctrines and Christian doctrine, please watch the two videos below. They are very helpful for understanding these vital issues. I don't share this to try and bash members of these religions, but to point out these people are lost in false, dead, works-based beliefs, and desperately need a Saviour. They are every bit as lost as the friendly Atheist or Muslim. And worse, they think they know the truth and hold to Scripture, when they have in fact fallen for lies.
Mormons:
http://www.youtube.com/watch?v=WzXazxES4mk
Here's a great video of a Christian witnessing to a couple of Mormons:
Video Footage! Talking to Mormon Missionaries On The Street! - YouTube
Jehovah's Witnesses:
http://www.youtube.com/watch?v=-Mr-Q1mRkUc