SIU - Special Investigations Unit. Delta Green, FBI, whatever.
Trace minerals as in the exact mineral constituents of a human being.
Key to making this weird is there are obvious signs of a previous investigation once the characters begin for the "second" time - from the players perspective this is the first time. Just to reiterate - BEGIN PLAY NORMALLY FROM THE RED ARROW, DO NOT PLAY OUT ANYTHING ABOVE THE RED ARROW
Memetic memory loss as in - you forgot, and anyone talking to you about the thing also forgets.
Up to you how the house attempts to consume/deal with them. Weaponised architecture feels cool, but equally architectural antibodies or something weirder. Go nuts.