Post a few pics of your tank. You can easily put a few rock caves in a 3 foot wide tank, which should help limit the aggression. My larger Midas never claimed the entire territory of 500 gallons, just its cave. It doesn't bother the other smaller Midas, as long as it stays away from the cave of the larger one. I suggest providing as much hiding spots as possible, so that each one of the Oscars can claim there own territory.