Theses two ladies are all over the place! Just jumping around, leaping from one place to another. Don't let them get away with this Faithful and Discreet Slave question. Make them investigate it and have them give an "answer" cause apparently, they don't sound too certain about this. After all, you are the Bible study that they're suppose to convert, they should follow the way you feel most comfortable with, not the way they like it. Also, tell her that it's rude to interrupt or just point it out to her politely and stick to the main subject.
The doctrines that reject hellfire, trinity, immortal soul are nothing unique to JWs, you can find these same beliefs in other religions, specifically ones that originate in Adventsim like Christadelphians, seventh day Adventists, Church of God, etc. By pointing out that others teach this, you can ask: if the Faithful and Discreet Slave, supposedly directed by Holy Spirit, provides these essential "bible truths", why do other religions which are not suppose to be true, teach it as well? It's good to remember that Charles Taze Russell had Adventist influences.
http://en.m.wikipedia.org/wiki/Adventism
Theres this blog you can check out. It's a Christian guy who is having a study with and Elder. They discuss and debate different topics like new light and the FDS. It might give you some ideas on how to tackle them.
http://blog.evidenceministries.org/discussing-new-light-with-a-jehovahs-witness-elder/