Logic for availabilities to communicate/ interact with one another.

Once X is booked Y becomes unavailable

Once Y is booked X becomes unavailable.

We are looking to apply this logic to two separate products using two separate events and availabilities

The current constraint we have is differing attendee limits on the two events. I would like Y to become unavailable when 1 attendee books X, rather than once the 20 attendee limit is reached.