@Jane3259 Under the current Extenuating Circumstances rules, your normal cancellation policy would apply in this situation. A temporary fuel shortage would amount to a transport disruption along the same lines as road closures or train cancellations, none of which are covered by extenuating circumstances.
Assuming that Airbnb isn't going to override you here, it's up to you how you want to help the guests out - a date change or partial refund via Resolutions would both be generous offers. But of course, the guest could have also bought travel insurance that covered unexpected disruptions like this, so it's no obligation on your part.