I'd say your guess that it's probably a tour group buying out the plane isn't so far fetched. I've had that happen before in Egypt as well. Last time I was there ASW and LXR were all Embraer RJ flights but looks like now they've upgraded the aircraft slightly, but still easily within the scope of a Nile Cruise offload. Aswan is a common endpoint for those. As much as I hate to say it, you're probably going to have to compromise on your plans. I wouldn't count on the tour group cancelling any of them until the very last minute. You could get a driver to Luxor or one of the Red Sea airports perhaps, Hurghada or Marsa Alam? But I don't think that would really help if your schedule has that narrow of a window.