I'm trying to find songs that would work well for an unusual casual brass ensemble:

• One person who actually learned to play trumpet, but hasn't played much in a while. They can read well, but their easy range is now just Eb4 to Db5 (F4 to D5 thinking in Bb) and they can't play too fast. A few notes below that Eb4 are probably fine, but not too many.
• Two or three people on baritones (octave below trumpet) and maybe Eb tuba (octave and a half below trumpet) who don't read music and just want to fool around.

This means we need sheet music, to be read with C as Bb, but also songs that are well known enough that others can just play along. The only sheet music we had on paper was Bach duets, which failed this second category, so we spent most of our time looking online for sheet music, which was less fun than playing. We did fine a few that worked, though:

When the Saints Go Marching In

Johnny I Hardly Knew Ye

(Several other things didn't end up working well, mostly because we found bad sheet music or they were the wrong range.)

Looking now, a few other things that I think would work would be:

Oh Susanna

You Are My Sunshine

Yankee Doodle

What else would be good?