You can of course give a full refund if you want, but you are not required to give it. Instead, you can choose to adhere to your set cancellation policy, to which the guests agreed when they booked your place.
The extenuating circumstances is of course a different matter, but assuming that the booking was made after March 14, 2020, it is unlikely that the guests would qualify for that EC policy.
@Greg523 if the guest is ill she can obtain a medical certificate and present this to airbnb for a full refund under their EC clause. For other reasons, she will be refunded according to the cancellation policy under which she booked.