You have overstocked your tank and if you do not get rid of most of the fish they will all die. Goldfish are very dirty fish and produce a lot of waste. They need an air pump and filter as well as frequent water changes. They more you keep together the faster the ammonia, Nitrite and Nitrate will build up poisoning them. If they are small you can prpbably keep 3 if you started the tank correctly with starter bacteria. Take your water to your locak fish store and have it testes reguarly. Good luck!