@Bill1150 If the guests were responsive to your message, you might have an opening to offer a date change with a big discount as an alternative to cancelling. Even this would be a stretch, though, if the guests' plans were based on the Christmas holiday.
The renovation delays, although not entirely within your control, don't appear to count as "extenuating circumstances," so the cancellation penalties are probably unavoidable. But the longer you wait to push that through, the harder it will be for the guests to find somewhere else to stay. Getting it over with ASAP seems like the right thing to do.
Also, your calendar is showing availability for dates earlier than 21 Dec., so until you fix that, your guests will have a hard time believing your excuse.