I took the trunk lock cylinder to a locksmith. He was able to create a good working copy out of the lock cylinder. Now my doors can open and close with the key.
Sounds to me like you're using the wrong key. It would be unusual for all the lock cylinders to be stuck at once.
I don't think you can access the trunk lock by removing the taillight. All the key lock does is turn an electrical switch that activates a solenoid on the trunk latch.