well every oscar i have had was totally mellow, as long as no one bothered them they didnt bother anyone else (including tiger barbs that they could have easily eaten but were with since they were little so left them alone) and yeah you are def going to want ot move up to a 100g AT LEAST 6ft 125 would be good, the bgk will get to about the same size as the O so just them by themselves would be pushing it in a 60g once they are full grown, fullgrown O needs a 75g to be comfortable IMO but as long as you get the larger tank before they get bigger then a ebjd temperament wise should all get along fine