Cheating ruins last few weeks

My last few weeks of school were ruined by confrontations with my principal over student cheating incidents and his interference in our union vote.  We had 4 of our students cheat in 2 separate incidents--all were officers in CSF of which I am co-advisor.    A couple of months earlier a teacher had had an incident where students had been working on a homework assignment which involved test corrections.  One girl gave her paper to the other one who copied the work and problems--not even realizing they were different versions of the test.  the parents of the girl who gave her work claimed they had worked together and that she had't intended to cheat.  Our CSF policy states that both parties are equally guilty and lose their membership for the semester.  Eventually the parents threatened court, the district and principal backed down but maintained that the teacher had not done anything wrong.   Consequently, the principal changed policy without announcing it--he no longer allowed the deans to give the CSF advisors any academic code referrals--but the teachers for the last incidents came directly to us.  In one instance, the girls copied each other and worked together--later claiming they thought it was a group project.  In the 2nd instance, one girl copied the other completely and when the teacher ran it through "turnitin.com", it came back 100% plagiarized!  All 4 girls were officers in  CSF and knew better than most students what the academic code meant.  The girl that copied the statistics project 100% went to my co-advisor and confessed.  they were all good people that did a stupid thing.  The principal said that after his investigation, none of the girls had the intent to cheat and that we needed to reinstate them.  I asked him about the students whose parents hadn't called ---wasn't that an inequity?  He told me to reinstate them and I refused...told him he could. The final straw was at graduation when he gave the principal's award to the one girl who confessed to cheating--out of 33 other valedictorians!