@Carol0
You can cancel a booking and face the host cancellation penalties - not recommended if you want to stay in business !
You may contact airbnb and ask them to cancel if you are uncomfortable with the guest, but quite honestly I do not think your reasons are valid. And we have to accept a few "bad" ones occasionally - not all guests are perfect, they are human after all. And what is wrong with sightseeing - this is what tourists do and it keeps them out of the house and out of your hair during the day.
I would write to those guests again and have them confirm their arrival time and whatever else you require. If there are issues or unresponsiveness, you could consider contacting airbnb.
Perhaps consider changing your strict cancellation policy to moderate. This way guests can cancel free of charge if there is a bad match.