Hi J.
Wow, twin boys, school and work! How do you do it? That is truly amazing!
Have you tried going to Micheals (50% off) or some craft store that sells halloween decorations? I don't know how scary you should make your stuff. They'd probably just love it if you had a costume party! You can ask that all the kids to wear their halloween costumes. Make one of those touchy-feely black boxes where they can't see what it is they are touching. Brains-cauliflower, worms-spahgetti noodles, eyeballs-large grapes.
Dangle bats/ghosts/skulls from the ceiling!
Make a haunted corner in your home for a picture back drop so the kids can get a picture with a mummy(you) or a scare crow (another parent). Drape it with a black cloth and black lacy material, make cobb webbs, put fake spiders and bugs and a witch's broom in the back of the corner.
Decorate your front door as they walk up to your home with scary halloween stuff. Pretty much the same way you would with that haunted corner!
Do the old fashion games. Drop the clothes pin (painted black and green) in the jar of creepy toy bugs. They get three chances. If they get one in they get a prize. (Halloween stickers)
Do the gift bags with toys of bugs, candy, party favor stuff.
Hope that helps.
I need suggestions on my daughter's first birthday...boys are so much easier! lol