I too do not like raining on other's parades, but we are all here to help each other, and not being honest is not going to achieve this. And there may be new aquarists reading these threads, assuming they too can make the same mistakes if we say all is well.
It would certainly be better to have more discus, minimum 5 or 6. As they mature, they will assert their natural behaviours, and a larger group allows this to work itself out better. Adding fish to the existing group several months down the road may or may not work, larger tank or not.
Second issue is the temperature. Discus should have warmth. Jack Wattley, who probably knows more about discus than anyone alive, says 82F is absolute minimum. The apistogramma may be OK with this--what species do you have? But the glowlights will not. And most corys will not last; Corydoras sterbai is one that will, which is why it is frequently suggested for discus. But the majority of cory species prefer cooler temperatures, 76/77/78F being absolute max, as for the Glowlight Tetra. Please check all this in the profiles. And if you do, you will note that 82F is the high limit for Glowlights. But fish should not normally be maintained permanently at the high end of their range; they are better mid-range, with the high end being OK temporarily, as during summer heat waves, etc.
Another aspect is fin nipping by tetra. Many species will take advantage of the sedate discus and apistogramma to nip their fins. And, the smaller the group of tetra, the more inclined they are to do this. If you are going to stay with the discus and apistogramma, on this issue alone I would re-home the glowlights now.
Byron.