Contact Airbnb, have them cancel penalty-free because the guests said they will not be arriving within your set check-in window.
I hope you kept all communication on the Airbnb messenger - that is the only evidence Airbnb will acknowledge.
You don't need to worry about alternate accomodations for those guests. You need to focus on getting the booking cancelled penalty-free ASAP. The rest is up to the guest and Airbnb.