Scary idea, but what if this was a failed attempt to make porn? And their plan was to invite a few sorority sisters to house sit in a big beautiful house, so of course they’d bring their boyfriends for some couples alone time, take long showers in their fancy bathroom, skinny dip in the pool, or something else porn-y?

You said that owners had video cameras; maybe these cameras were better quality than the normal rich person home security system. And maybe the changes to the house were either the owners themselves or some other associated person checking the cameras or some parts of what would be the background scenery.

It would certainly explain their irritation that no one spent the night, as well as their refusal to pay even though you and your friend did the chores as they asked.