Neither of your lenses are good for the job. Can you borrow a 16-35 mm f/2.8 L, or a Tamron 28-75 mm f/2.8 or 17-50 mm f/2.8? How about a Sigma 24-70 mm f/2.8 or 18-50 mm f/2.8?
You can use flash, but don't use flash when the band is playing. Some bands may not say anything, some bands may scream at you. However, NO band likes it, and it's a bit disturbing for them while they're trying to play.
If you're taking a photo of people enjoying themselves, then you can use a flash. If you can bounce it off the ceiling, it would be better.
To shoot the band from near the stage, you're really going to need a lens that goes anywhere from 24 to 80 mm. ANY lens that gives you some zoom in that region is good. You likely won't need any focal lengths outside of this, although a 100mm f/2 or 135 mm f/2 is great for shots far away. Your 70-200 mm f2.8 is also good.
My biggest recommendation for you is to buy a cheapo Canon 50 mm f/1.8, and shoot the band with that lens.
If you can't borrow any lenses that cover this focal range, then I'd use the 10-20 mm for people photos, and 70-200 mm to shoot the band. With the 70-200 mm set at 70 mm, You're not going to be able to get whole-body shots if you're standing in front of the stage. If you can stand 15 feet away from the DJ/band, then 70 mm is going to be better.
To shoot the band, you're going to have to use shutter speeds of 1/60th of a second or faster (preferrably 1/100th seconds if you don't want motion blur), and you're likely to use ISO 800 to ISO 1600 the entire night. I'm just telling you now so that you don't stand there for 5 minutes, trying to figure out your settings.
Actually, just set it to ISO 1600 at the beginning, or AUTO ISO if you can. Use Shutter Priority(!!) Also, when you take portrait photos of the band or DJ, adjust your focus spot so that you focus on their face. If you're standing very close to the stage, Don't use the centre focus point to focus on the DJ's/bands face, then recompose the shot afterwards. You won't get great focus of the DJ. If you're standing a good distance away, then you can do this.