Not following how branding one child or one parent troublemakers helps the coach who complained. His objective is to safeguard his position. He doesn't want a rival coach 'turning heads', taking on the teaching of other young skaters , luring them away, correct? How is that achieved by complaining about you? How does telling the other parents that you are a troublemaker help him to keep the work which is with those other parents' children or safeguard him from the risk of the other parents giving their children's tuition to this new coach ?
We still don't know what words were used either. You summarise the words by 'trouble causers'. Surely, that alone would not mean anything to the other parents? If I said 'X is a trouble causer' and no more, the reader would be none the wiser; it doesn't tell them anything. I would have to say something of what the actions or words were. What are the parents supposed to do or think if I don't tell them something of what the trouble caused is?
What trouble , what things were you doing or saying, had he to complain about and , more importantly, what did he say they were ?
PS. I was amused by your calling your daughter 'a minor' and yourself her 'representative'. I have never heard even a lawyer describe his own child and himself as 'a minor' and representing her; it is lawyer's language, but we only use the terms for clients and litigants, not ourselves :) Must try it on my own.