Staff member can only be assigned to 1 booking ID per time slot 📅

We require an option to only allow a Staff member to be assigned to 1 booking ID at a time, per time slot.

Example:
1 Hour slots – 2 staff members can be booked during this time slot. Each staff member has a capacity of 1-4 people.

• Booking 1 = 10am / Staff member A / 2 people
• Booking 2 = 10am / Staff member B / 4 people

Currently BookingPress allows another booking for Staff Member A - as there is "2 spaces" still available.

We need an option to NOT ALLOW this to happen.
As there is already a booking for Staff Member A - they SHOULD NOT be allowed to be booked again.

Thank you