this is always a thorny issue. Unfortunately, some trainers work undercover to avoid any kind of profit sharing. You use the term “our trainers”, and from that I gather that you do not have trainers as independent contractors. Is that correct? Trainers often resort to that kind of clandestine operation when the gym does not give the option as an independent contractor.
Trainers who typically work as such are also ‘out there’ they have a web presence and are not invisible. If they are trainers with a business, I would approach them directly if what they are doing looks like training rather than being workout buddies.