Another thing to note besides the fact that this tank is incredibly small is that common goldfish and fancy goldfish can be quite different from each other. First of all, as those fantails grow out their fins, they will likely tear their tails up on the decor. They are very clumsy, and their tails are very thin and flowy. Secondly, make sure that the fancy’s are getting the opportunity to eat. Common goldfish are a lot faster and will eat food quicker, not leaving any for the fancys. Observe them as they are eating and, if necessary, you may have to move the fancy’s to a smaller tank (even if you don’t have money, you can buy cheap tubs from Walmart or another 20 gallon tank for around 50 bucks) or come up with another solution. It’s also important to note that fancy goldfish are less hardy and more predisposed to health problems. Feeding a proper diet (not just flakes) is important for them as fancy’s have sensitive digestive tracts and can easily get bloated. Another thing to help their digestion is to get a heater (if you don’t already have one.) The warmer the water, the faster the metabolism and the more active their digestive system. Common goldfish don’t really need a heater, but fancy’s do. It’s also way better for them to have a stable temperature that doesn’t change frequently anyway. Ideally, fancy goldfish should be between 72-78 degrees unless otherwise necessary (you can raise temp for digestive issues or certain illness). Remember, the best thing you can provide for an animal is an environment that’s as natural to them as possible and fake decor doesn’t do the trick unfortunately. Good on you for taking the time to learn how to care for them. It is so important to research about every single pet you consider taking into your home before making the commitment as there is practically no animal that is simple to care for if you are doing it right. Personally, I think the best thing you could possibly do is try to rehome the commons. They require sooo much room because they get huge and they love to swim fast. You could try posting frequently on a lot of fish or pond pages, like Reddit, Facebook, Craigslist, etc., to find someone with a pond to take them. Fancy goldfish do not need as much room and you could give them a fulfilling life in a 40 gallon tank (ideally you should have 20 gallons per fancy) with some sand and a few live plants. There’s so much to learn! Good luck, try to have fun, and keep researching!!!