The mandolin and clarinet have compatible volumes. The clarinet is tuned to a C major scale and the mandolin is tunable, so they can be played together. The clarinet is usually thought of as a melody instrument, but I am taking advantage of its low range to play backup to the mando.
The xylophone was designed to play chords and can play all the chords in C and F.
The flute can play in both C and F as well.
The dulcimer can play melodies, chords, or both. It's a bit quieter than this flute, so the flute player needs to watch the balance.
Marimba bars change pitch a bit depending on temperature and humidity, so I had to tune the fiddle to the marimba. You can hear a few notes that aren't quite right, but it's still fun!.