Angels can work, but not all the time, they would need enough space should they want territories separate from each Discus.
Corys are entirely peaceful and fine with Discus.
Clown Loaches however will get very large and may well be too active and boisterous for the slow-moving Discus, especially as they grow. Clowns ideally need to be in groups of 4-5 or more in a minimum of a 6ft tank.
Balas are in the exact same boat as the Clown Loaches, they are very large growing and active, they will bother the slower Discus as they grow.
I would rehome the Clowns and Balas and get a couple more Corys instead (depending on tank size of course).