I have had the oscar for 2 years and never had a problem with aggresion. People always talked about the aggression, and I honestly thought I had a real oddball dopey oscar, that is until the jag cichlid was introduced.
Oscars aren't really aggressive when compared to other cichlids. People tend to assume aggression because they eat other fish. I would either go South American (keep the Oscar and Chocolate) or Central American (keep the Jag and Convict) because the Centrals aggression is a lot higher than South Americans. Also Oscars thrive when they are not the low man on the totem pole!