Hi @Tami1
To me it sounds like you really want this booking. Pets can cause a big mess, but it's limited to their abilities as pets. You have to weigh it up against losing this booking that you want. If you decide to go through with it, in addition to what the others have said:
1) Try to see what furniture they could scratch, and try to make a plan. (Perhaps your guests are bringing a scratch pole. It may help, but anyone who's successfully taught multiple cats to scratch in one place is not me and not someone I've met)
2) Block you calendar a bit at the end, just to give you time to assess the cleaning situation. Keep in mind future guests could be allergic. Cleaning may not be as bad as you think, but you say it's a quiet time anyway and you can always open nights up again when all is done.
If you want the booking, you should probably just make things work around the cats.