On the legal side of things they should not be favoring one employee over the others because you are not being equal or fair to the other employees to make additional money. The other issue is that Eddie threatens to fire Jane because she finds out that Eddie is giving Greg all the higher end tickets that make better commissions than any other. The higher end commissioned tickets should be distributed equally so that everyone gets a chance to make extra money and not be singled out.
You would not ever threaten an employee to fire them by telling the truth that is unethical and bad business. There is employment laws on wrongful termination and harassment. Believe in this case that if Eddie fired her than it would be wrongful termination because she was doing her job and doing it well. Just because she tells Brad that Eddie is favoring one over the other is not grounds for termination. Also believe that she is being harassed about her job that would be terminated if she told.
This is a from of harassment because Eddie would probably continue to mention not to say anything or she could loss her job. The other employment law that Eddie is doing is discrimination. He is discriminating other employees to make extra commissions. Also it may make the company look bad if the same person does those jobs and then leaves that position you need to have equal opportunity for all to make the same amount of extra commissions as everyone else.