I would start checking things out at the wiring harness in the rear. The wiring for the rear lights runs down the driver's side in my car (hopefully yours also), so remove the panels in the rear on that side and look for the harness.
It is strange that both rears went out at the same time. IF the brake lights work, then the problem is likely to be the hots. If the brake light doesn't work, then check grounds and hots in that harness. The ground for that harness should be bolted to the body somewhere back there.