You can put just your comet goldfish in a 100 gallon tank. If you want to place all of your fish in the same tank, it will need to be much bigger than 100 gallons. You will likely need to build a pond to house both of your goldfish. Is Sparky the red and white fish? He looks like a Ryukin to me. Ryukin goldfish require a minimum of 40 gallons of water. If you can afford a 140 gallon tank for those two fish, great. However, your pleco makes things difficult. Most plecos cannot live with goldfish because they require a heated tank while goldfish do not. I would absolutely take all your fish back to the store, cycle your tank, and add the correct number of small fish. If the store will not take your fish, you can sell them on a site like craigslist.org/ or you can give them to friends with fish ponds.
Not all the fish in your tank will show the same symptoms. It's likely that the comet goldfish has a better immune system than Sparky. You need a liquid test kit in order to monitor water parameters. High ammonia, nitrite and nitrate are silent but deadly killers. Please buy a liquid test kit and post your readings for ammonia, nitrite and nitrate.
If by Cycle, you mean the bacteria in a bottle, that stuff is worthless unless it is refrigerated from the time it ships from the dealer to the time it gets to the store, to the time you bring it home.
This website
PlanetCatfish • the online home of aquarium catfishes will help you to find out what type of pleco Hoover is.
Also, you need to change the water every day with that many fish, especially goldfish, in such a small tank. In a well-established 140 gallon tank with two goldfish, you will only need to change the water once every 1 to 2 weeks.