What an encouraging tale! Thank you for telling it so well. How sheepish those two must have felt after you had finished with them.
Their circular arguments and standard responses become mind-numbing when trying to get down to particulars, like getting them to answer direct questions. Your reasoning about human reasoning is something they've probably never considered. My JW mother used to insist that the Bible could "interpret itself." I would reply that it's impossible for a book to interpret itself, and that what a book requires is a human brain to read it and therefore make an interpretation. And that humans, being different, have arrived at different interpretations of this text. I also tried the logic that if God created the human brain, wouldn't God want the human brain to be used, like for thinking and such. (No, apparently.)
I so admire the research you've done and the way you directed that conversation. I especially like the way you referred to a paragraph you allegedly hadn't read yet! They must have been absolutely flummoxed.