You clearly know that what you say you are seeing is unacceptable.
If you have facts and are prepared to stand by them, then you also know what you should do. If you don't have facts then get some.
If you choose to walk away and 'not get blacklisted', you also have to live with the consequences when, if all you say is true, the inevitable happens.
I am not normally prone to be judgemental, but in this case I would suggest you act like a grown-up and as a pilot who has a due sense of responsibility. Confront the school's CFI and manager with your concerns, and if they do not respond appropriately, send an honest letter to the CAA which you would be prepared to discuss openly around a table with the company and with the CAA reps, and which cannot be used against you in a libel court.
BW