He is super malnorished, and that is why he is sick. Orandas should have round bodys, like your other orandas and fan tails? Im assuming those are the other types.
http://www.aquariumfish.net/images_01/oranda_red.jpg
I see two problems. One, it looks like you have either a shubunkin or a commet.
http://fetes.seneffe.be/theme_economie/independants-et-commerces/services/monclus_etangs_st_feuillien/images/800px-shubunkin_goldfish.jpg/image
These fish are very fast and will get to the food before the others have a chance.
The second one is the size of your other fish. They all look very large compared to the small sick one, and will also get to the food faster.
Your little guy is basically on the bottom of the feeding pole, and therefor not getting enough food. I would recomend buying weekend goldfish feeders. These are the white discs that you throw in the tank and they release food slowly for several days. I would just always leave one in the tank. This way, he can eat whenever, and isn't competeing for the foor with the other fish. Also, try giving them different foods as well. things like squished peas, lettuce, sliced zuchinni, and sliced oranges are excellent for your goldfish, and they will gobble them up. Frozen bloodworms and brineshrimp are good, and are also great for fattening up skinny fish.
I see nothing wrong with any of your other fish. They all apear fine. Your large one is swimming perfectly fine. thats how goldfish swim. In short jerky movements.
Also, "swim bladder disease" is misnamed, as it has nothing to do with their actual swim bladder. Goldfish get swim bladder when they swallow air, usually while eating. A lot of people feed goldfish floating flakes. When they go to eat, they gulp in air with the food. The air cannot escape from their stomachs, and they lose control of their boyancy. This causes them to swim or float upside down a lot. I ALWAYS recomend sinking pellets. They are better for your fish, and reduce the risk of swim bladder. If you insist on feeding flakes, stick your hand down in to the tank before releasing them, so the goldfish are not eating from the surface. Sometimes swim bladder goes away, some times it does not. But I have seen fish live 10+ years while affected with this.
http://farm2.static.flickr.com/1002/907158368_034f4fc550.jpg?v=0
This fish is alive and otherwise healthy, but will spend much time just floating at the surface upside down
But your little guy doesn't have that. Like I said, he is just EXTREMELY underweight.