On Halloween, keep your buns cool and quiet, away from the constant noise and activity of Trick or Treaters.
Close the windows and doors. Close the blinds to avoid flashing lights.
Play music - peaceful, easy listening (not loud). Think elevator music.
(No hair bands or hare bands. Stay away from 1812 Overture.)
Your TV service might even have a suitable channel in its lineup - you just never tune to those channels.
If you do not already have boxes for them to play on and in, get some plain cardboard boxes (not slick or a lot of ink/color, no staples, labels or tape); cut at least two openings in each box big enough for your bunny to get in and out. They can hide in them, to further mute the noise and feel a little safer.
An air filter in their room may provide white noise to help muffle Halloween sounds.
Keep them company and reassure them that everything's okay. Pet them if they are the petting kind of bunnies. Have a couple of healthy rabbit treats handy (Bunya told me to say that). But keep them away from the human treats and candy - these can make your bunny deathly ill.
Have a fun and safe Halloween!
P.S. Check out the post Bun o' lanterns -- Bunny pumpkins for Halloween