Also, I need to check the FAQ. Is it across the board that investigators at the same location can trigger another investigator's asset or threat actions? Or is it just the threats?
Just threats - check the rules for the Activate Action entry in the RRG:
"Activate" is an action an investigator may take during his or her turn in the investigation phase.
When this action is taken, the investigator initiates an ability that specifies one or more icons as part of its ability cost. The number of icons in the ability's cost determines how many actions the investigator is required to use for this activate action. When performing an activate action, all of that action's costs are simultaneously paid. Then, the consequences of that action resolve.
An investigator is permitted to activate abilities from the following sources:
- A card in play and under his or her control. This includes his or her investigator card.
- A scenario card that is in play and at the same location as the investigator. This includes the location itself, encounter cards placed at that location, and all encounter cards in the threat area of any investigator at that location.
- The current act or current agenda card.