Jack Brothers are a "Punk Jazz" band from Gothenburg and they consist of:
Johan, Jonas and Stefan.

They have released 13 albums this far and
are still active (according to their website http://www.jackbrothers.nu/ )

The lineup are (most often):
Saxofone
Bass
Drums

The name (jack brothers) were given to them by a drunken man who walked up to them whilst they were playing in the street in down-town gothenburg.
The man apperantly first asked them about the name of their band, when they answered they had none he said something like "why dont you call yourself jack brothers then". Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.