Nice to see the photos, and glad all's going well.
For small fish, I find Fish Science Tropical Fish Micro Granules (slowly sinking; natural formula with insect meal) ideal, as they're the smallest pellets I've seen, red in colour, and therefore easily taken/consumed - I'd recommend these as the best option for your ember tetras. Aquarium Munster / Dr Bassleer's Biofish-Food (regular) are also very small pellets but, being brown in colour and sinking, they sometimes fall fast before they're noticed - but your embers would likely enjoy those that they do notice/reach and they'd be ideal for bottom-dwellers or those who eat from the bottom (your cories but not your embers). Fluval Bug Bites Tropical Formula for small fish (insect larvae and salmon recipe fish food) are good too but seem to be slightly bigger and more difficult to chew, brown in colour, and so are slightly less easily taken/consumed; you could pre-soak these to make them easier to chew but then they might fall faster and be missed by the embers.