Ok the covered corals can recover. If the cup is dying it has a slim to no chance of recovery. They are known for it. Dependig on it's contition, toss it. Clean off the corals as best you can and let them recover. And do a PWC
for good measure.
Crashing? I wouldnt say so! Just going through a rough patch! Try not to worry. It will be fine!
Edit: i read 2nd post. If its brown jelly, get the affected part out asap. The other corals should be fine. What are they mad about? The powerhead? I dont think thats a couse for death but i dont know the whole situation.
For the angel you can try not to stress him and feed foods soaked it garlic, or you can move him to QT and treat with copper. Your choice, but make sure it isnt just sand on him