Hello @Beth6111
How frustrating.
Airbnb have shared this self check in information with guests like this 48 hours before - for at least the last three years so it's nothing new.
I'm afraid it's your responsibility as the business owners to provide guests with individual codes so this can't happen.
when the guests who should have been staying were locked out on arrival were you not able to sort out your codes directly to give them access?
the guest who turned up on the wrong day shouldn't have been refunded.