If you still have doubts about how to defend yourself, here's my little guide to help ya
1- if some of them get in your office activate your camera tablet and deactivate one of your cameras to make it go away. The camera you just deactivated will be back after some time. Headless goofy isn't fooled by it tho, if he appears you can only hide under your table to make him go away. Speaking of it, hide under your table can be used at anyone, but you chances of surviving are 50%, so it's more safe to use the camera trick.
2- Donald Duck (or Daisy) head can appear anytime in your office. When it appears, quickly deactivate a camera, or else you just going to get deaf by it's sound and will make all the other characters present on that night to move faster than normal.
3- If you start to hear Suicide Mouse piano on the background, it means that he's going to appear sometime. Just do the same trick like the others and you should be fine. The song will remain but after a while it will stop.
If you still have some doubt about something, just reply here and I'll try to help you. Good luck