you are giving very little information about your current status. Do you already have a business with clients or are you just starting from scratch?
If you want to keep employees, it has to be a give and take. Since you use the term ’employee’ and not ‘independent contractor’, I assume that you plan to provide the trainers with the equipment they need to train and also the training directives. You would do the marketing, all the financial transactions and have a worker’s compensation policy.
When starting such a business, most people start with another trainer they know already and trust. The concern about ‘stealing business’ is valid but is more likely to happen with people you do not know and who feel no allegiance to you. You would have an employment contract which typically contains a non-compete clause.