I know this is late, @HelenRu, but when it comes to The Mother of All Fancy Dress Fiestas, the sky should be the limit. A piece of advice: now is the time to start playing the opening song to "The Nightmare Before Christmas." Boys and girls of every age/Don't you wanna see something strange?.....
. It should put you in the mood.
There is so much you can do. So very much. There is one rule you must stick to and it is, "I must not try to blend in." The bigger questions I have are, "What is your wildest, craziest fantasy?" and "What would it take to get my husband to go equally nuts?"
Part of the point of Halloween is to turn all social rules on their heads. Go for it, girlie!!
For the rest, I shall direct you to Amazon.com because whatever you do, you should buy makeup. A great costume for your husband would be "The Chef from Hell." Required: Fake blood in large amounts, Spirit gum (this is an adhesive) kits that are made to create scars, old nasty meat cleaver, white apron, fake limbs (hands preferred, foot acceptable) and chef's hat. Optional: pick up the proper face paint to make hubby look like a ghoul in the face; there are tutorials on YouTube and there's time to practice.
Another for you would be the zombie. Go get yourself the nastiest, mankiest set of torn clothes and at least one shirt made of flannel. Save an image of what the dance squad looks like in the music video for Thriller: you will notice you are going to have to concentrate the weird grayish purple colouration for spots on your face that are boney, similar to what you would do for a skeleton. (Don't forget to do your neck and hands, too, and if you use grease paint, don't forget the setting powder so it doesn't get all over everything! Otherwise, you will need some sort of flour or talcum powder, super strong hairspray, manky ankle boots that may be a bit too big, and fake blood (the kind that you can swallow; if you can't get this, you shall need Lyle's Golden Syrup and copious amounts of red food dye.)
As a zombie, you are going to WANT to look dirty. You are going to WANT to tease your hair up so it looks like Edward Scissorhands or Albert Einstein and you are going to WANT to have fake blood oozing out of the corners of your mouth. You WANT the big heavy boots so that when you do that stilted gait they make a heavy boom on the ground...and you are going to WANT* to rasp "Braiiiin....must have braiiiin to eaaat."
You can do the witch thing, but, it won't be worth it if you look like all the other witches that shall be there. (Where is the fun in that?) You can get some bandages, a fedora, some aviator sunglasses, and a trenchcoat and poof! Instant invisible man. But nothing beats scaring the daylights out of your friends by coming out of the shadows and demanding to eat their brain to go with your drink!