Use the same unit for bookings and leases. The calendar stays in sync with Airbnb and Booking.com, so availability is always clear.

A unit does not have to be locked to one model. With leaser the same unit can support both bookings and leases, without the calendars colliding.
Two-way iCal sync keeps availability identical across Airbnb, Booking.com and your own site. A server-side check stops two simultaneous bookings taking the same date.
Set the rental mode for each unit and decide which flow is prioritised. Add min and max nights and length discounts where they fit.
One unit, every rental flow, no double-booking.