There are serious stocking problems here that need to be sorted out. This means questions.
What are the water parameters, being GH, KH and pH of your source water?
What species are the "yellow cichlids?"
While waiting for this info which is crucial to any advice we can offer, I will mention that the two angelfish are not suited for a 40g tank. I know they are small now, and a larger tank may occur...but plans for larger/more tanks do not always come to fruition, and it is not fair to the fish to acquire them before you have a permanent life-long home. Depending upon the gender of the two angelfish, you may have serious issues waiting to spring up. I'll return to this aspect below.
The bush fish should be your main resident, and every other fish suited to this fish's requirements. This includes water flow from the filter, plants, dim lighting, parameters...lots to consider. But as you like the bush fish and intend keeping it, and it is OK in a 40g, the other inhabitants must be suited.
Now to the general aspect. When we put "x" fish together in a tank, they will react usually according to their genetic programming which we cannot change. While one would normally expect this or that behaviour in such circumstances, it may not always come about. The environment, both the good (favourable) aspects and the bad (inappropriate combinations, inappropriate decor, etc), does impact how a fish reacts to various circumstances. I don't know the cichlid species here, though I suspect being "yellow cichlids" they may be rift lake species, and this is a deadly match for angelfish and bush fish. The fact that you may not have seen physical interactions to make this obvious does not mean the fish are not suffering the consequences. Fish communicate via chemical signals, pheromones (read by others in that species) and allomones (read by fish in other species) and these can cause serious stress if they are negative. So please do not make the mistake of assuming that because you do not "see" trouble, it is not there. It is. Fish do not change their inherent genetic makeup to suit us.
The two angelfish, if they are both female, or if they are a male/female pair that have accepted each other and bonded, might be OK for the moment (ignoring the obvious serious issues of the other cichlid species). Adding two more is almost guaranteed to cause problems. This species is a shoaling fish, that live in groups and develop a pronounced hierarchy within the group, and they do this fairly quickly. In their natural habitats, the vast expanse of water means this plays out without incident (unless a fish becomes belligerent or ignores the dominant fishes). In the very small confines of even a very large aquarium, this can play out very differently. A group of no fewer than five must be introduced to a tank together, at the same time. How their hierarchy plays out depends upon circumstances and the fish. Right now you may not see any issues between the two, likely due to their fear of the yellow cichlids--which again you may not see, but it can still be there. We are dealing with living creatures that have evolved in species-specific ways, and this may play out according to the norm, or not. One should never hope for the exception, but expect the norm.
