I would do more of a "Disney bounding" look rather than full on costumes in the heat. Focus on shirts that either have a character or are a certain color and wear a couple accessories that help to pull it together, like ears or a hat, a tail, stuff like that.
Pirates- plain white shirts that you cut notches in all the edges of, paired with an around the waist sash, a bandana, and an eyepatch (push it on your forehead so you can see).
Little Mermaid- you as Ariel and DD as Melody with each of you wearing a mermaid themed shirt, matching ears, and mermaid sequin slap bracelets. I've seen bathing suit cover ups at Walmart that look like mermaid scales that you/DD could wear over shorts to give a more mermaid look. DH could be Prince Eric wearing a regal-looking t-shirt like posted above and blue shorts or a white shirt, blue shorts, and red sash tied around the waist (for when Eric is dressed less fancy). DS could be Sabastian wearing a red t-shirt and a red hat with crab pinchers coming off it, or Flounder with a yellow shirt with some blue stripes painted on and a blue mohawk/headband/hat.
Mickey, Minnie, Goofy, and Pluto- Wear appropriate ears or hats for each character. For Goofy and Pluto the hats with each character's dog ears would be cute. For Mickey, a black shirt and red shorts. For Minnie, a red and white polkadot sundress and large bow. Goofy could be an orange shirt with (thin material) black vest and blue shorts, and DD could be Pluto and wear a yellow sundress with a green belt to resemble Pluto's collar.
Superheroes- For Capt America, blue shorts, a blue shirt with a star (or the Capt's shield), a red and white striped sash tied around the waist, and a blue bandana with an A on it around the head. Hulk could be frayed purple shorts, a green shirt with muscle ridges drawn on (or one of the Hulk shirts that has the printed muscles) and a green hat or dyed/sprayed green hair. Ironman- shiny gold leggings (cut into shorts/capris so it's not as hot), a red sundress or shirt (again, they make some that look like his chestplate), and a red hat with gold accents to resemble his mask. For Spiderman, get one of the shirts that resembles his costume and wear blue shorts with it. Add in a fake tattoo of a spider or spider web for good measure.
Incredibles- red shirts (or sundresses for the females) with the Incredibles logo on them and black shorts underneath. You could get plain black sleep masks and cut eye holes, but you'd be pretty recognizable without too.
Toy Story- Woody could be jean shorts, belt, short sleeve yellow plaid button up shirt tucked in, and a bandana tied loosely around the neck. Cowboy hat optional. For Buzz, wear a shirt themed like his chestpiece and white shorts. For Jessie, they have shirts printed like her shirt and the top of her shorts, and then you/DD could wear black and white cow print leggings/shorts under and have hair in a braid tied with a yellow ribbon and a headband with a small red cowboy hat attached. One of you could be one of the aliens with blue shorts, blue shirt with a planet on it and one of Disney's Alien hats or headbands.
