Far fetching theory..
I don't know if this has ever been mentioned...but homes constructed in the decades proceeding the event sometimes had bomb shelters..They were common during homes built in the 1950's-1960's... and even promoted by the government heavily after the Cuban missile crisis..Some homes had hidden shelters in the back yards or basements with secret entrances..
Is it possible that they discovered an unknown shelter or secretly knew of one on the property? If that were the case I am thinking they could have entered the shelter and became locked in accidentally.....Bomb shelters would be underground and sound proof...and their bodies would remain there today...