That's what I get for typing like crazy, posting and then coming back to read.

Below is what I typed is Ammonia isn't the problem here. It MIGHT still be relevant.
FishDin is correct, Ammonia burns could account for all of this, and is a simple answer, much more likely than what I thought below.
There's a virus found in angelfish from the 1980s that wiped out a lot of fish, like 80%+ of those infected, it was like a plague and there's been some reports on here this winter from a few that came across it.
In the hobby we call it angelfish aids, it's been identified as viral hematopoietic necrosis (VHN), (translates something like "viral caused blood cell death")
It can be confused with Ich or parasites at first, but instead of it taking a while for ich or parasite symptoms to get progressively worse, the fish rapidly declines in a couple days to death, the fish usually gets ragged fins and a dull mucous coating over their bodies, they get white spots and usually sit "nose up" and can be on the top or bottom but usually sitting on the bottom of the tank, unlike with gill flukes where the fish will always be at the surface.
With VHN it can look like parasites or ich at first, the fish rapidly declines, and then organ failure and death, all in just a coupe days.
the immune system kind of fails with the virus, opening the fish up to secondary infections,
the virus takes hold, blood circulation declines which causes the rough appearance of skin and fins,
and then bloodcells collapse and organs fail and the fish dies in the majority of the cases.
The other fish types being sick too though,,,, I'm not sure about, Discus get it, so do angels, I've heard of gourami getting it. never catfish though....... I'm thinking the catfish might have been unrelated cause of death though.
I was thinking Lymphocystivirus, but it wouldn't touch the cories either. if it were Lymphocystis it looks rough but the fish rarely dies from it it's mostly cosmetic and tiny pus bubble cysts that heals up in a couple weeks and goes away.
I think this is what your angels had though, VHN "angelfish aids" and if so, you are pretty stuck for like 6 months before getting more angels or anything that had died from this outbreak in your tank just to be safe or you risk new fish getting infected, the virus can survive in the tank for somewhere between 3 and 6 months. you'd need to break everything down, and sanitize with lysol everything then clean it up again to remove the lysol after it's killed off the viruses, and even then if you aren't thorough and miss something the virus can still be there. Most people write the date down, keep what they know don't have an issue with the virus, and watch the calandar for 6 months before trying again any of the species that were affected from this outbreak.
Some try again after 3 months of waiting. and have had success, but also some have had reinfections.
Safe and easy bet is to wait the full 6 months and just steer clear of the species you know were affected.
For sure, no angels and no discus. cichlids in general will be a risk, the gouramis are likely off the table unless you can chalk it up to a different cause. the cories...... That still perplexes me. might have been something else that caused that....