Like lions on the savanna, all the fish you have chosen occupy a similar alpha status in their watery habitat, in nature. You have chosen all competitors, so trying to keep them all in the same tank (especially a tank as small as a 55, even temporarily) is like trying to keep lions, tigers, leopards all in the same tiny cage, and expecting thing to be nice.
In nature you might find 1 pride of lions, and millions of wildebeest in a many square mile area.
In nature a pair of Jack Dempseys will guard an area of 250 gallons.
When Jack Dempseys share habitat with other cichlids, they often suffer, even in thousands of gallons of water.
If you are new to cichlids, get 3 or 4 of a single species (maybe either JDs or GT's) and grow them out in the 55, and instead of other competitive cichlids that are almost guaranteed to kill each other, get a shoal of the geographical correct dither fish (the wildebeest equivalents of the fish world). These would be live bearers like mollies for JDs, or tetras for GTs.
Below is a video I took in Mexico where because the JDs share habitat with other cichlids, their population is small, and they are torn up.
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now a video where JDs are the dominant cichlid, and share habitat with only live bearers and hardly any other cichlids, and their population is larger, and they are healthier. Also note the space available
Eden2