1- I agree this is the best of the three shots you posted. Nice composition, nice framing. I like seeing the Zidjan logo from the drums.
I like the use of depth of field, but I find that the drummer himself is a bit out of focus, which is mainly seen in his hair / eyebrows. I thinking this is motion blur, maybe from having a shutter speed too slow. Do you remember the settings you used? Or as you said for the third picture, the shirt collar seems more in focus than he is
2- Same as above where nothing seems to be in focus. I'm thinking its a too slow shutter speed / camera shake. The composition is off, which you pointed out, as she is cut. There is alot of "dead" space in the middle of the frame and on top of the frame. Maybe wait for a more action moment where she is closer to the mic and singing in it. She seems more at rest than in action.
Watch the backgrounds as well, as you can see a bag (her purse?) If she was singing and you moved in closer, that would solve the background bag issue
3- Nice composition on this one. I like the somewhat downlow angle. Again the picture is suffering from lack of focus / motion blur, which is obvious in his hand.
Seems like you are doing good with getting the pictures together, focus on the tehnical aspects of getting proper focus with the light that you have. Increase your ISO, open the aperture, get more light...all in order to get a faster shutter speed to freeze the motion more.
As for the focus issues, I personally don't use the autofocus as much as I use the single point focus. I set it to single, aim the camera at what I want to be 100% in focus, hold the button half way, recompose and shoot.