Why is it that you think the two will grow at different rates and not the dozen? I'd have thought it easier to control the food intake with two?
There is a guy on YouTube 'the Do It Yourself King' or something like that. he has a tank of 6 feet with 6 Oscars and a Pufferfish all seemingly doing well.
After researching quite a bit i reached the conclusion that a 5x2x2 would be a good sized tank for them when mature. Now i have them, i'm finding more info questioning that.
Mine Oscars are only small today, bought seperately, one about 6inches, the other around 5. They get along fine for the most part but did have their first scrap a couple of days ago. I read that a rearrangement of the aquarium can stop it. I did that. They have stopped. I do realise that these fish are not even sexually mature yet. Thanks for any thoughts/advice.