My two boys have recently started playing and I'm looking for beginner Christmas arrangements that we could perform as a trio. Could be a mix of skill level but ideally mid level to beginner.

Thanks for any suggestions

I've mentioned this one before. Kjos publshes a set of books called "Christmas Time". Carols in 4 part harmony with 1st always playing the melody. You ccan buy 1, 3, and 4 in bass clef (but not two -- wonder why). 32 carols in easy arrangements that could be used for caroling outside or in Church.

There's lots more stuff for trombone trio in easy to medium forma. I hope others will chime in. Especially with jazzy or rock styles.