I have no idea as to your knowledge level, so I will offer some comments that I hope will be of value in understanding fish behaviour. Chances are, the fish are not getting along. The inherent behaviours and requirements of a particular species of fish are part of that fish's makeup, programmed into their DNA. When we put them into an environment that does not provide for these, it causes stress, and as the stress builds, it begins to harm the fish's health. Fish don't have many options to deal with this; they either accept it (which almost always means an early death) or they fight back somehow. Physical interaction is one way of rebelling, but fish can also release chemical signals that are just as stressful to the other fish, making things worse and worse.
Ironically, the very small space here for the fish may be why they appear to be managing; the physical space affects their behaviours considerably, and to the detriment of the fish. It is like a dog kept locked in a small room, never let out; the dog becomes more and more frustrated, and can react by becoming very aggressive, or the opposite, literally wasting away.
The only way we can ever assume that fish in an aquarium are really getting along and are healthy is by providing each of them what it expects, in terms of the physical environment, water, numbers, other fish, etc.
