@Bonnie331 Are you permanently closing your Airbnb, or is this a temporary measure?
If it's a permanent closure, I would just let Airbnb know that you're no longer able to operate and ask them to assist your guest in finding other accomodations. They should not penalize you: it would be a similar scenario to selling the property.
If this is temporary and you will try and host the space again in future, I would contact Airbnb anyways and ask them if they will give you penalty-free cancellations and assist the guests to find new accomodations. Unfortunately, the Extenuating Circumstances policy no longer covers illness (see Extenuating Circumstances Policy - Airbnb Help Center) but you may find a sympathetic customer service person who will work with you.
Don't do any cancellations without speaking to Airbnb first. If you do, you'll be penalized financially and will have cancellation reviews placed on your profile.