They are in a 60 gallon right now. They will be here for about 6 months and then I will put in my 180 gallon tank. Ideally, yes, more would have been better to disperse aggression, but that is all Wetspot had left. I do not want to mix them with a scalare type because they will cross-breed and dont want that.
Right now this guy is trying to let the others now where their territories are. Discus do it too, although the Angels appear to be more aggressive toward each other than even discus.
I have been keeping two groups of keyhole cichlids. The first group of six which I got from the LFS were aggressive from the start even when they were not full grown. It may have been because of the cramped conditions in the store and limited food. I suspect they were relatively old for their size.
It turns out, of this six there was one male and five females. I believe the females were fighting for dominance. A pair formed and then the real aggression began. (Now it was 2vs everyone else, instead of 1vs.)
I separated the breeding pair who produced a batch of fry that I raised. I kept eight of the jueveniles with the two parents in a 75g and there was only intermittent aggression while they were smaller.
What I found was that as long as the children stayed out of sight for the 3-5 days that the parents attempted to breed, once they got it out of their system, the aggression disappeared and they would all shoal together again for two weeks. I eventually had to separate the parents to their own tank because beyond a certain point, their offspring wouldn't stay hidden, the parents never attempted, and it was weeks of non stop chasing.
The eight fry are now full grown and they get along amazingly well as a shoal in the 75. I think I have 4m, 4f based on relative size and body shape.
I'm sure you've witnessed variations of this in different species. I'm just sharing my story because you might find it interesting.
The point of all this is that cichlid aggression seems to be a combination of factors. If a group of siblings are brought up as a large shoal, without any food competition, in a large enough tank, they may stay friendly and not attempt to breed. With a larger number the chance of pairing is going to be less, imo.
Its probably impossible to know the psychology of wild caught fish.
My guess is that if there is enough vegitation to allow them to effectively hide without being visible, and if they are not attacked during feeding time, there won't be any damage or prolonged aggression. Keyholes can hunker down and camoflage themselves to become invisible. Angels probably can't hide as easily.