Mutual respect throughout the exchange. It could have turned negative very quickly but your astute mindedness paved the way for a helpful exchange. I like that you did not zero in on their specific beliefs as JWs but centred the exchange around beliefs shared by most Christian believers. They were less defensive and would even concede your points.
I've no doubt that these two JWs will remember the exchange and may even have thought far more deeply on the issues that came up. Well done!