I actually had to give away one oscar because they tried spawn so many times they were causing stress on themselves and tank mates to often. They stay close to each other lip lock and one cleans a space over and over and they will wipe their bellies on the surface and fan it to clean it. This can go on for a while before dropping their tubes. But i would def recommend a larger tank.
Their nesting area is pretty big. My preference is to have at least 50 gals per adult oscar. And 150gals per spawning pair. Now, that's just my preference.