I think it's time you sent your family over to this forum to express their views. I'm sure we could set them straight.
I'm going to tell you a little story now - you may want to pass it on
It's true and I think it may make it simpler for non-fishy people to relate to fish.
I once knew this guy who lives in France. I can't remember exactly where but it was just outside Paris and we've unfortunately lost touch now. Anyway, he was a great character but severely disabled. He is a distant relative I think as it was my cousin who introduced him to me and mentioned something about him being related to my aunt or something. He explained that he had a rare inherited genetic disease. Can't remember the name for the life of me. I'm certain a google search would turn it up. He is about half my height and I'm about 1.63 so he looks like a dwarf height-wise. However, he also looks abnormaly bloated with ordinary arms/legs etc but 'lumpy' body. He has to use a wheel chair to move around and his sister has to take care of him and all the jobs around the house because he cannot get up and move around. He is destined to die young which is unfortunate considering he is very clever and great company. When younger, he was completely normal. It was as he got older that it became apparent he had the disease. It was eventualy found that what he has caused his body to stop growing. His internal organs continue growing normaly though. He needs operations and medical help to keep his vital organs working and part of his lung had to be removed when it colapsed due to being crushed against his other organs as they out-grow his body.
Obviously, that doesn't sound nice or pleasant so I hope this old friend won't mind me using him as an example to help you and others relate to fish being stunted...
Now consider this is what happens to a goldfish when kept in a small bowl. Unfortunately for the goldfish, there is no medical help available and no loving family or friends to help make life more pleasant. A stunted goldfish will grow to the size of the tank, true, BUT, it's internal organs will NOT. Eventualy the fish's organs are crushed. As this happens gradualy, the fish slowly wastes away. At first it seems normal but it slowly begins to appear bloated. Sometimes you can't tell at all. Eventualy the poor fish has to suffer the slow, painful death as it's insides out-grow the outside. Would you want to have this on your conscience? Are you aware that a goldfish can easily live for 40 years if looked after properly?
The guideline with goldfish should be 1 fish for 20 gallons and then 10 gallons added for each additional fish. As such, four fish need 50 gallons. Granted, fancy types don't grow as large or live as long. HOWEVER, I personaly take this guideline to be for the fancy types. Comets, shubunkins, sarasas, commons and some of the larger fancy types need 20 gallons per fish or more. I would think a pond is much more suitable. Remember these fish get to 12".
Considering that no one would keep a 12" oscar in less than 75 gallons, even if completely alone, I think suggesting a goldfish can live in a 20 gallon is being very generous already.
5 gallons is out of the question.
*drowns out what I think of her generally with funky rock music*
