I studied for 2.5 years. I know how it works.
Be polite. Respect what they're saying. Act like a willing student...someone that wants to understand where they are coming from. In reality, you will learn a lot from them, how they think, and what JWs are about. This will actually help you. Learning about JWs here really doesn't give you a complete picture. Ask questions as if you are genuinely curious how to resolve the logical dilemmas that the info brings up. Not like you're trying to trap them. It may take a bit of damage control to get back into the "non hostile" category, btw.
To be prepared, use the Lingle Bible Teach link I mentioned to you before.
If they don't answer to your satisfaction, just look troubled, but seemingly not wanting to cause too much of a disruption over it. Ultimately they will want to move on. Their thing is that once you get the "big picture" all the little pieces of the puzzle will all suddenly fit together. Politely allow them to do move on.
Also, you have to be selective on what to ask about. Save up for a good one, but don't stop to analyze stuff too often or be "nit picky" or else they'll want to separate you from your wife into two separate studies...Because you're too slow! Also try not to get too sidetracked into off-topic doctrinal stuff. Ask if such and such doctrine will be discussed in the book later on. Defer discussion on that topic until "we cover it".