Welcome to the community, @Lisa5958!
If I were you, I’d accept the guest to stay for few days and let both sides consider the extent of to monthly stay.
Of course, the guests need to make the booking through Airbnb. In the same period, guests indeed to know the place is satisfied or not.
Since Airbnb is guaranteed for the first-month stay payment, and the guest need three months to stay,
I’ll advise the guest to make the three bookings, reservations monthly and explained this would be the safe ways.
That’s always a place to improve.