They weren't actually Greek either, they often changed identities by getting new passports and shit.
The older guy was "The Greek", we never got an actual name from him. Spiros aka Vondas was his partner, and The Greek would be his advisor/boss. Vondas would be the one to meet people, make the deals, the set-ups, the connections.
They brought drugs, guns and prostitutes from other countries to Baltimore through the Docks who were ran by their guy, Frank Sobotka. The shit was taken to a warehouse, ran by "Double G" George Glekas (the one Ziggy shot).
Prop Joe sold the drugs wholesale to the other dealers, that's why the Greeks liked him so much and one of the reason why he started the Co-Op. Because he would order drugs for all the other dealers and The Greeks wouldn't have to worry about meeting all the drug dealers and worry about who's cops and shit like that. Joe took that responsibility.