Aggressive Danio

Personally, I would exchange the remaining danios for more harlequins. Both are shoaling fish and need a minimum of six, with more being better. And danios, depsite their size, really need a bigger tank. They are such fast swimmers that they are more suited to a four foot tank.
When shoaling fish are kept in insufficient numbers, the alpha fish has only a few others to pick on. With larger numbers, the aggression (which is quite normal) is spread out amongst more fish so not one individual gets too much.

You also need more cories. Bronzes do get quite big, so maybe get 2 or 3 more rather than four (though that would be better). The dwarf cory species (pygmaeus, habrosus and hastatus) are more suited to smaller tanks. I have 7 pygmaeus in my 50 litre.