The angelfish should be removed ASAP. Angelfish and discus should never be housed together. For one thing, angelfish are more aggressive, but aside from physical aggression there is feeding aggression. This means the angelfish are more determined ("aggressive") feeders and will easily out-compete discus for food. The discus then slowly waste away, and may stop eating all together just from fear.
Silver Dollars need a group of at least six, but (a) there is not sufficient space here for them, and (b) they should never be combined with discus or angeelfish.
To explain more about angelfish, as another member said they may well beecome nasty. Angelfish is a shoaling species, meaning it must have a group, and with angelfish it should never be fewer than five. Two, three or four angelfish will eventually result in a "bully" if one of them is a male and there is another male; the only exception is a bonded male/female pair. Angelfish must select their mates and bond or there will be trouble.