Perform La Bomba 2 on both Ravel and Debussy and then unleash godhand immediately. Considering you have some of the strongest punch techinques equipped, a single unleash should be enough to take out the remainder of both of their lives, leaving the 2nd one with only a little or none left. If he's not dead yet, take him out as fast as you can to avoid interruption by the 3rd one (the other guitarist) who joins the battle after of the first two dies.

Against the last dude, break his guard and spam High Side Kick cancels against the wall until your TP is refilled. Then unleash and finish him off.