Did the guests ask to change the reservation and refund them for the two nights they won't be staying? Or did they just notify you that they plan to leave early? It makes a difference in guest satisfaction and expectations. Airbnb support can clarify for you what will happen if you or they put in a request to change the number of nights, and the other party accepts. The Airbnb system will automatically take care of the amount of payment by following the strict cancellation policy. You will always have the option after the stay to refund any amount you wish to, or not.
You can choose to follow through and be strict about the cancellation of the last two days, or you can choose to be more accommodating. I would suggest you compromise with the guest and modify the reservation in a way that will make it a win-win, and give the guest a reason to be grateful. Afterall, they will be staying at your place for 9 nights. Starting off with a good rapport will likely result in a great stay for the guests and a higher chance they will take good care of your property. Think about building positive travel karma! What goes round comes round.
You have a beautiful place in a great location, which should be easy to rent. However, I see from your listing that you rarely host guests. Is that because you don't offer to, or because guests choose not to book? With strict cancellation policy and a 5 day minimum stay and a significant cleaning fee, you may be limiting your potential bookings and earnings.
Good luck with making your decision and hosting your guests in a way that will make their trip memorable!