I'm trying to write some simple stuff (kind of) for brass marching band and not entirely happy with how it sounds. (But this might be because of the MuseScore sounds.)

I have a trumpet playing the main melody and main voice. A cornet is following the trumpet, harmonizing the whole melody below.

I don't know at all what trombones usually do in marching bands. I'm talking about tenor trombones. I thought of doing fewer notes, and emphasizing the first note of each measure to create a kind of inverted chord sound. Also, I'm not sure how long the notes should last or how they should be sustained in general.