These performances by the Monster Quartet, aka the Easy Listening Monster Band, were produced in the 1980s for the Sesame Place theme park in Langhorne, Pennsylvania. From the Muppet Wiki:
The music features solo performances with light accompaniment from each member, consisting of Maurice on trumpet, Kermit the Forg on trombone, Clancy on saxophone, Bruce on keyboard and xylophone, and Elmo on guitar. In other segments, Grover replaces Elmo in the band on flute and Ernie replaced Bruce on the keyboard. While these pieces were originally produced exclusively for Sesame Place, they would later be used as Muppet segments on international co-productions.