Residents still aren't allowed back into the evacuation zone, but a firefighter was able to check out my sister and brother-in-law's property and give them a report and some pictures.
The house is gone. From the pictures, I can recognize the burnt-out remains of the washer and drier, the hot water tank, and the stove, but there's obviously not anything left that can be salvaged.
On the bright side, the shop (a prefab metal structure) looks fine. Even the shelf outside the door, holding flower pots and other bric-a-brac, looks undisturbed. If you didn't pay attention to the charred hillside behind the building and the smoke still in the air, you could look at that picture and not realize that it was in the middle of the disaster zone.
Besides my BIL's workshop and a rec room, that building has a full bath and a spare bedroom on the second floor. Once they're allowed back into the area, if they want to move back onto their property before a real rebuilding effort is arranged, it should be possible for them to occupy that space. In a lot more comfort that the folks now living in an unofficial tent city at the Chico Walmart have...