Hi @Serena322 I hope you are well.
What a nightmare situation.
Adding a co-host to a listing doesn’t allow for the co-host to take over the listing and for it no longer to be associated with you, they are merely allowed to operate it on your behalf.
When you add a co-host you agree to the terms, such as being responsible for their actions on the listing etc, so I’m not sure what you can do in terms of reinstating the cancelled bookings- get in touch with Airbnb customer services ASAP and see what they suggest.
Paul