I've had 2 tiger oscars in a tank for over 10 years. They are now 14" and 12". 1t about 8" each they would fight terribly, tearing fins off, skin wounds, etc. They always healed, only once did I remove one of them for a few weeks to heal and stop the fighting. One time they knocked a powerhead off the uptake tube and it ended up pointing up, draining about half of my 150 gallon tan out of the top!
I've had many tankmates with them and never had any problem as long as the other fish was larger than their mouths! I have a 12" Pimelodus Cat in there with them and he gives them hell all of the time...circling around just to chase them. I now have the oscars, the pim cat, a Disticotus Lussoso, 3 Tinfoil Barbs (3+"), and 3 Lg. Silver Dollars, and a 6" Adonis Pleco.