If people aren't feeling good, nothing gets accomplished. The solutions, then, need to recognize this reality. Leadership is crucial. At least it gets rid of uncertainty which feeds anxiety. If the head is not fully behind the evaluation process, the process is doomed from the outset.
Accountability is a professional obligation.
Research shows that people are willing to be accountable when the process is thorough and fair. Pick your volunteers carefully and involve key others as peer evaluators. Since you probably have supervisors who also teach, they should be among those early volunteers for the teacher evaluation process. The approaches to evaluation are legion. A whole industry has sprung up of people selling different methods, instruments, videotapes, and workshops.