This is possible with VariableTriggers, create an Area then have a variable for the amount of people in the area. Increase and decrease that...
This is from the developer console from Chrome: Failed to load resource: the server responded with a status of 500 (Internal Server Error)...
Can't save groups for some reason. Could this be a problem with https? I tried the exact syntax from the image to make sure I'm doing it right...
Separate names with a comma.