Welcome to the forums JPatrick! God bless you and your wife for teaching NFP. Some of us are only called to be promoters, so we are thankful for those called to be teachers!
You are getting some great feed-back here and I agree with all of it. I would say, as a six year user of NFP, your phase 2 length is a little concerning. From my original research in Marilyn Shannon’s Fertility, Cycles, and Nutrition, it sounds like your wife might be having some health issues. The very low libido during her progesterone phase makes me suspicious too. We have a long phase 1, a 10 day phase 2, and a 10-12 day phase 3. Even when my cycles have a broad range, this is still pretty standard. You could be presuming phase 2 when she might really be in phase 1 but suffering from background mucous. These are all things worth looking into.
The knowledge of NFP is something to share with everyone with great joy. The application in our individual marriages is something only God truly understands. The lack of honeymoon is not because of the knowledge inherent to NFP. It is something else. I would agree that it might be the 5 kids and their current ages.

Does your wife have a high libido during phase 2? If so then maybe 5 is supposed to be 6.

I am really just teasing there because I have no idea of your present circumstances. I commend you for your generosity in having a big family!
The thing I really love about NFP is that it can root out problems. In every situation I have encountered, NFP was never THE problem. But it tends to highlight what the real problem might be. Is a couple selfish? NFP will reveal that. Is a couple working against God’s plan for them? NFP can reveal that too. Is a couple called to adoption? NFP can help discern that too.
The knowledge written on our bodies is so amazingly helpful. As you know as NFP teachers, it is the application of that knowledge that is to be applied with much prayer and self-sacrifice. God bless you for teaching. I hope you are able to use this particular trial as an amazing witness to the gift of our sexuality. You’re both in my prayers.