A goldfish is a cold water fish, so it does best when it is in cooler water. Any goldfish forced to live in a tropical fish setting will probably live, just like you can live outside when it's very hot in the summer, but it will not be the healthiest, happiest goldfish it can be, just like you would rather be in the air conditioning.
They "can" live in warm water. Goldfish are "Coldwater" fish. They are actually a species of Carp that evolved in cold water. They come into breeding condition when water temperature gets above 65F. They breed at just below 70F. Warmer temperatures will shorten the fishes life, weaken them and make them prone to disease.
No, the tropical fish will probably eat it
Goldfish may be kept in an uheated fresh-water aquarium. They are considered ill-suited to live in a heated tropical fish tank, as they are used to the greater amount of oxygen in unheated tanks.
shouldn't be a problem because they live in both
they are found in collection tanks around the world but originally found in China
If the goldfish is a fancy variety, it can live alone in a 20 gallon tank. Goldfish do not belong in tanks any smaller than this as they grow very large
Probably, but usually the comet goldfish will get all the food and/or the other goldfish will become miserable. This has happened to me before and I do not recommend putting them in the same tanks. Try putting the fancy and comet godlfish seperate!
yes
yes
goldfish do not live on land
No, fish can't hear.
yes
totally in tanks I've had a fish in a tank and in a bowl and the tank ones lived longer
Three in a bowl? To live its full lifespan a goldfish needs ten gallons, so if you want three, you need to have a 30 gallon tank. Or 3 individual 10 gallon tanks. Otherwise they will live a month, maybe.