Most of your links mention that tetras help the discus, plural, school and not one by itself trying to school with the tetras. Still nothing about same level fish.
Most schooling fish have a pecking order. There's always a alpha male/female out of the group who will pick on the other males/females.
Don't you also have angels with your discus?
i dont think your supposed to keep juvenile angels with discus bc they can transmit some kind of disease.
So what's your final stock now? I'd be here forever if I read the whole thing...
55g is too small for discus
just saying...