Karen, since the culprit in this case is not AirBNB, but booking.com i suggest you take this matter both to AirBNB and booking.com. Also try to explain it nicely to the guests, maybe send them links to this forum so that they can see it was not your fault, maybe they will understand and they will cancel.
This is the response i got from booking:
"There currently is a bug out with our Calendar systems where our Partners can not Export Calendar or Sync accurately on other platforms.
We have our technical team currently working hard on trying to resolve this issue. When they have resolved they will send out a message to all of our partners stating so."