What is the collective name of a musicians and robbers?

There isn't a single, commonly used collective noun for both musicians and robbers. Here are some options you could consider, depending on the context:

Playful/Humorous:

* A cacophony of crooks

* A rogue's gallery of virtuosos

* A band of merry outlaws

* A symphony of thieves

More Serious:

* A company of performers and criminals

* A gathering of musicians and lawbreakers

Ultimately, the best collective noun will depend on the specific situation and the tone you want to convey.