Real Hack-job Photoshop skills coming out. I threw this together real quick as an idea of subtle differentiation.
This can be what some rooms look like when they are
empty
View attachment 3251802
Notice the lights in Ema's Room, really this is the only thing changed in this group from the original pictures
And when the rooms are
OCCUPIED
View attachment 3251804
Note the lights in Ema's room are back on (as before). The steam in the 2F Bathroom indicating someone is inside, and the door in the 1F hallway being open. Real small changes that can benefit someone who is paying attention or looking carefully. I'm absolutely sure you could make better changes. But this is just a proof of concept as it were.