I was pretty frustrated with many of the flute duets for Christmas and Advent season being pretty simple. My older students still wanted to play Christmas Music, but wanted them to be challenging. So I created 8! The melody goes back and forth between parts with each phrase. They're great for student-teacher mimicry and neither part gets bored. You can listen to each duet (live recording) and see the first page of each score.
Here's a link to the duet collection (You can also buy them separately!) http://spottedrocket.com/ChristmasDuets.html
Duets included are "God Rest Ye Merry Gentlemen", "Jingle Bells", "Silent Night", "Coventry Carol", "What Child Is This?", "O Come, O Come Emmanuel", "Jingle Bells", "We Three Kings", and "Pat-a-Pan".
Enjoy and Happy Playing!