Cichlidsman555:
I want to say this, beings I have raised Jacks before.....
1. If you have all of these fish together in the same 55 gallon, you could run into trouble. If the 2 Jacks are both male,when they mature, they will fight for territory even if no females are around, if they are a "matched pair" (male/female), they will defend their territory to the death with the other fish.
2. The Convicts will battle the Jacks for tank space, they seem to like the same areas to "hang out".
3. All but one of these fish can reach up to 15" in length, the odd fish out is the Jewel (6-8"), it will become food, it isn't agressive enough to defend itself.
4. In about 6 to 8 months, you will find out that a 55 gal isn't big enough to house all of these fish together, there will be fighting amoungst the cichlids, the Oscar will be stressed out, and the Jewel will disappear.
I hope I have answered your question.