What are the dimensions of the tank? It looks a bit on the short side for 2 female cacatuoides (so might be better to go for only one).
I already tossed my gourami out of the tank because it's super shy and a stupid centerpiece if it always hides, i may as well get rid of the danios too then, i just used them for a fish in cycle seeing as they're super hardy.
With this attitude, you should not go anywhere near Apistogramma or any other fish for that matter. Just because the Danios could survive the ammonia and nitrite, that does not mean that it has not affected them, and since you mention hardy and cycle in one sentence, it is pretty safe to assume that you did not cycle safely.
Gouramis are only shy in the wrong environment. Going by the photos, your tank is a wrong environment for gouramis.
As for changing the ph, mine's about 7, pretty neutral, i could do more bogwood and some beech leaves to lower it, the lemon's would enjoy that, but they've been with what i've got. I heard apisto's needed around 6.5.
Bogwood and leaves would be appreciated by the tetras, Corys and Apistogramma. No fish "needs" exactly one pH or another, as no body of water has a pH that stable (at the very least, it fluctuates throughout the day). What soft water fish very much benefit from is soft water (low GH). They can live in neutral water, but they may be slightly more susceptible to disease in that.
With cichlids it gets tricky. […]
What you don't realise is that Apisto's are usually harem fish, so a male and 2 females usually work out very well. Often the male will breed with one female then the other. A pair of Cacs would be fine in your tank, as would a trio.
minnnt is absolutely correct:
Apistogramma cacatuoides are a harem species, although I would not say that they usually are. I observe that most Apistogramma species that I come across breed in pairs.
I don't see anything wrong with keeping one male. A lone male will not die because it's lonely. Apisto are not schooling fish. They are found in colonies in the wild were each male has his own territory.
You've just contradicted yourself there
and actually, it is possible for a fish to die of loneliness and it happens more often than most people think. At the very least, the Apistogramma male will behave oddly on its own, just as a schooling fish will when kept on its own. All Apistogramma are social fish and this particular species is a harem species.
What you are saying about the behaviour is correct for even more social and aggressive species like angels, discus, rams and keyholes, and for unsocial cichlids like green terrors, jack dempseys, etc.
This tank would be a one male territory. Add 2 males and it could be constant war.
Correct, which is why we are recommending only one male.
You should change gravel to sand (for Corys at the very least, and Apistos if you ever get around to them), and add a lot more cover. A plain, dark background will also help. Until you move to live plants, increase the number of fake plants, going for silk ones.