You're the one thats misinformed. i recommend you read up before you start posting nonsense ****.
When a fish is in a tank thats too small for it, its body stops growing, causing it to have internal damage, etc.
Goldfish are COLDWATER fish, while BETTAS and GUPPIES are TROPICAL. They live in different temperature waters and eat different foods.
Also, goldfish are one of the MESSIEST fish around. A 14 gallon tank simply CANNOT support 2 goldfish for more than a couple months.
Unlike our friends, JDonner, I have experience with Goldfish.