The JD's may or may not be a problem. They usually don't bother larger fish. But exceptions to every rule. I was warned by several not to put my pink convict in with an O. ½ said the O would eat him, the other half said the pink would tear up the O (they are known to do it). Regardless, I have them together without problems. 1 Oscar is 9-10" and the other is about 12". They are both approx 1 year old- 1½.
If you start them out together young, they might stay together without problems. You will just have to keep an eye on them.