Can you trigger several monsters at once?

[Diz]

If you are referring to actual storymode content, the gatherer which patrols after you find the elevator rods in the storage, then I think that is supposed to resemble the same gatherer which resided behind the closed door by the kitchen, deciding to take a stroll. The door might also be open after this event, even if you did not open it yourself, but my memory is vague as I have not played the game for a long while. ;)

When it comes to running from one monster spawn location to another monster spawn location, I do not think this will be easy to do in storymode. Of course, I may be wrong, but the last time I tried to do something like it, I failed.

If you mean in technical terms, like making custom stories etc. then I would imagine doing two triggers at once should be no problem, though I do not know for sure how the technical things of the game works.