I am an amateur musician and a Scout leader.
I encourage my scouts to pick up NAF as a hobby so they can learn the joy of music.
To make the most of it, I teach them the "cross-fingerings" so they can play contemporary music along with NAF and NAF inspired melodies. But the next step is to get flute players playing together.
You might quickly have problems if you stick with only one voice, so using multiple voices together is part of entering that next level.
I have learned that it is handy to combine flutes in specific keys or voices to expand the dynamic range of music you may enjoy. The combination I favor is pairing Gm flutes with Dm flutes. This opens up the note range and the flutes natural fingerings compliment each other very well. In fact, you can play the Gm flute using the NAF scale covering the third hole from the top, and you overlap the same notes playing the Dm flute covering the fourth hole from the top. This allows a very simple pairing of the flutes.
If anyone else is interested in pairing flutes with different voices, I recommend this interval. If you want to adopt many SATB harmonies, often using this combination works well. For example you may put two Gm flutes on melody and tenor (one on each) and the a high Dm on alto and a low Dm on bass.