Brake Problem 2007 Aveo LT

1) Parked in the garage for a about a week. Waxed the car and as I'm driving it out of the garage down a slight incline the rear right wheel is locked up. I stop and move forward again; same thing right-rear wheel is locked up. So I reverse gear and slowly back up. The read of the car rises up and I hear a metallic bang. But now the wheel is moving freely. But I'm concern.

2) Remove the drum the next day. The wheel comes off relatively easy. Upon examination I note that there is nothing obviously wrong. But when my partner pressed the brake pedal, only one side of the wheel cylinder moves. I take a rod and press each side of the cylinder to see if they both me freely; they do. So I try spinning down the adjuster mechanism to decrease the brake shoe diameter. No change. The other thing I notice is that neither shoe is touching the wheel cylinder. I spend some time adjusting the brake shoes, but for whatever reason, the wheel drum only slides on with the greatest difficulty. At this point I need to move the vehicle. And I know the wheel is gong to be locked up yet again. And as expected, when I moved forward, it locked up, and in reverse, the rear end rose up, but still spun with great difficulty.

Any idea what's going on here and what I need to do?

3) I need to replace the timing belt. I inspected it today and wonder if I need to unbolt the engine from the mount to get the timing belt off and on. Also does the serpentine belt need this too.

Thanks.