Have a hierarchy/logic for availabilities assigned to events

I work for a dog grooming business and have 9 events. 8 of them can accept 10 attendees (dogs). 1 can accept 4 attendees/dogs. I have assigned the same 10 availabilities to the 9 events, 4 of which are also assigned to the event for 4 attendees. If a customer books for one of the 9 events that can accommodate 10 attendees and is automatically assigned an availability that is also assigned to the event for 4 attendees, then that is 1 less customer than can book that event for 4 attendees. Ideally, I would like customers to book an event for 10 attendees with an availability **not** assigned to the event with 4 attendees first. If this can be solved, I have other businesses that I can bring to your app.