Now we're getting there. None of those fish are compatible which is the reason they're always fighting. You miiiight be able to get away with an oscar and green terror in a big tank, but even an adult oscar doesn't have enough jaw strength to fend off a smaller gt for long. Especially in a tank smaller than 100g because oscars are one of the slowest cichlids I've kept.
As for the others, shiners are a schooling fish so as an individual it's probably swimming around mindlessly and aggravating the cichlids. Shiners are also used as bait so I wouldn't be surprised if the oscar tries to eat it along with the pike. IME most bottom dwellers arent very good tankmates for cichlids unless they are much bigger, and even then they might eventually end up as a snack. It's generally not a good idea mixing CA/SA cichlids with africans like that blue zebra either because it will constantly pick fights with the oscar and gt until they get larger and overpower him.
So, I would recommend picking your favorite fish and build a compatible community around that based on your tank size. Then you can sell or trade in the others for store credit because even tho it might be difficult it will be better than watching them fight all the time and blaming yourself for it.
Also, if you're using stock hob filters from petco that could definitely be the cause of dirty tanks. Those cartridges they come with get dirty fast and don't leave room for bio media so I would either ditch them and use filter floss cut to size along with mesh media bags filled with biomax, or just upgrade to canisters or a sump when you can