but to be sure they be sexually mature you'd be looking at 6 x 10"oscars.
You'd need a 300 gl tank to make that work.
I had the same opportunity but i only wanted one, but later on i changed my mind.
And my Red is a real gentle 10"giant and i took a tiger from 7" and added him to the tank.
And i was lucky, for they showed no agression.
They actually formed a close pair.
Heres a video of one of the first days f them together, and all they did was impress: http://www.youtube.com/watch?v=IBvekHcolXE