Would keep an eye closely on water parameter's when adding fish .Depending on the size of the volume of water,,(unclear as to size of tank) .Adding fish can increase organics which Discus don't seem to tolerate well. Could also result in larger, more frequent water changes (unclear as to current water change routine).
Will assume the fishes are eating now and no longer listing to one side?
I had opposite problem with a group of Discus I kept. I had a total of seven,(blue cobalt,Red turquoise,Snakeskin, and Brown, but six of the seven would not allow a runt Red Marlboro a moment's peace.
I ended up placing the Red Marlboro in another tank.
Would agree that increasing the number's can help but Discus are Cichlids ,and will behave as such until a pecking order is established. They can be disturbingly rough with one another for an otherwise rather placid species.
Keep the temp warm, and your water clean.