Could gold feeder fish (normal ones) live with fancy gold fish?
You didn’t do the right thing in getting more goldfish. ONE of those “feeder” fish, also known as comets, can grow up to 18″ with the proper care and will need a bare minimum of a 75g tank with at least double the filtration. Not many of them do, just because people see them as extremely cheap, being sold for under a dollar, and decide to stuff them into bowls or tiny tanks. You should have at LEAST a 40g tank with double the filtration for your two fancy goldfish. Even though those “feeders” can coexist with fancy goldfish around the same size temporarily, it doesn’t mean that a fully grown fancy (8″) can then coexist peacefully with a fully grown common goldfish (18″). The size difference is just too great. Return the “feeders” if you can, or just give them away. Make sure your tank is big enough for the two fancies.