Girimama33-
We're going "Brave", as well! "Feast yer eyes!", as my five year old son now loves to say when he flips up the back of his kilt.....
(Trying to upload some photos of the costumes, but can't figure this one out....)
I don't know how sewing-machine-inclined you are, but my spouse was able to make some amazing dresses for our daughter and herself. Celtic-looking fabric is available online at all the big cloth distributors, like Joann's Fabric. We used leather for all the cords on the dress bodice and joints, purchased from Tandy Leather. (You can also get them from Michael's)
My wife purchased a great corset for herself at an online store called Damsel in this Dress. They have a large selection, and they have steam-punk attire, as well, which would work for your possible Minnie outfit.
My wife also made my two boys' kilts and shirts. She made all of the cloth portions of all of our costumes, with the exception of my kilt. My kilt is my real full-dress kilt, and I had it made from USA Kilts. I play the bagpipes, for a pipe-band, and for a Sheriff's Department, and so I already had most everything I needed for a "Brave" costume. My wife made the rest.
I made the sporrans (the little man-bag which hangs in front of the kilts), the belt buckles, belts, and kilt pins. (I made all the leather stuff, my wife did all the fabric....)
My little girl takes Irish dance lessons, and so we have a wig for her. You could go the same route. Just google Irish Dance Wigs, and you'll have tons of options. Just be warned, they can be very pricey. My little girl is blonde, and so we are just going with her natural hair color. It'll be easier, she'll still look like "Merida", but she'll be OUR Merida. Blonde.
We won't have to deal with the hair color bleeding onto anything (like our costumes or the characters), either.
There are tons of fun Celtic dresses/clothing on e-bay and
amazon. Lots of online stores out there, too, which sell Celtic, Ren-Faire, and period-type clothing.
We'll be in Disney from October 21-28, and we'll be going to the Halloween Party on the 23rd. Hope to see you, there! It'll be nice to see others in "Brave" costumes!
Also, my father and mother will be with us for the Halloween Party. While they won't be dressed up in a complete costume, I've given them little bits to wear. My mother will have a simple sash to wear over her regular clothes. USA Kilts has some photos of what I mean. It's simple and easy, and will put her as a definite part of our group. You could also choose from hundreds of different tartans, or plaids, to make your group a "clan" or family.
My father is a little more difficult, as there is no way I could get him to wear a kilt. So, I made him a simple kilt pin, and he's going to wear it like a brooch. Again, something small, but still makes him a part of our group. You're husband might go for a kilt pin on his hat. (USA Kilts, Henderson's Bagpipes, tons of other bagpipe equipment online stores) Or even a clan hat pin. Fairly inexpensive, and he could put it on his Boba Fett hat, too.
Good luck, and we can't wait to go!