As mentioned, I don't think there's anything that the Orc Musicians can do other than party. Here's things I tried to do-
*Played instruments while being turned into an orc and as a human
*Threw some rotten tomatoes
*Wore a party hat and used it
*Played a Party trumpet
Also note there's already an achievement you get for doing all the Orcsoberfest tasks/games. Unless this is some sort of hidden task or secret game that doesn't count of course. I think their solely decoration as sad as it seems. I discussed this with other friends and we came to this conclusion.