As a former JW, I can attest that this website (see link below) is the single best resource out there to show the JW’s doctrines from the beginning and how it has developed over the years.
jwfacts.com/
As a former JW, since I know how JW’s think, everything boils down to one and only one thing. Who has the authority bestowed upon them by Jesus Christ. This is the question that they cannot/will not answer. Always, and I mean always, when discussing religion with JW’s, make them answer where they receive authority and how do they know they can trace themselves back to the Apostles. Ask them where the “faithful and wise servant” mentioned in Matthew 24:45 was before Charles Taze Russell, the founder of their religion. Since they cannot answer this, well, you know where to go from there. This issue is KEY before any discussion can have any hope of developing. Do not get sidetracked by them redirecting the discussion to the Trinity, the Papacy, Mary, the immortality of the soul, etc, etc. Make them stick to the subject. Their own relgions publications paint them into a corner on this issue:
The Watchtower makes the claim that:
“Beginning with Pentecost, 33 C.E., and continuing through the 19 centuries since then, this slavelike congregation has been feeding its members spiritually.” Watchtower 1981 Mar 1 p.24
They contend that they are this “faithful and discreet slave”. They define their teaching authority, what they call their governing body, as this slave. And they claim it has been feeding other JW’s (or what they would call, “lovers of truth”) for 2000 years. Put the onus on them to prove it to you. Then I would ask them how about the bible and how we got it, tying that in with the question of authority.
Pray for them. They are seriously misguided people that have a genuine love for God.