i agree with icecube, but make sure you overfilter (at least 3x the filtration for your tank) and use quality food, like pro-gold by hikari.
I feed sinking shrimp pellets to my cories and loaches, and the goldish suck up about 8 at a time when I drop them in. They LOVE them!sinking high quality wafers or pellets are best.
With my *limited* goldfish experience, I'd agree that you have 2 ryukins and 1 black moor. As for them not developing right, I assume you're referring to your fishs' girths being much smaller than the ones in the picture? I have had a few fancy goldfish, and mine only got really "fat" once they had attained 3 or 4 inches. When they were young and small, they looked a lot like yours.
For three full-sized fish, I'd agree with a minimum of 50 gallons, and a filter rate of at least 500 gallons/hour, preferably more (either through one filter or by combining filters). I have a 6" red cap oranda and 2 smaller goldfish in a 50g, (along with a bunch of other small fish), and I keep the parameters ok by filtering at about 625g/hr (an emporer 400 and an enheim ecco 2236 canister), and doing a 30% water change weekly.