With my cories and only one female betta, I feed her when I feed the rest of the bettas and around 6ish PM, I drop the cories' sinking food in so that it is soft enough for them to eat by the time they get moving around - they are diurnal/nocturnal so they are most active early in the morning and around evening through night. With my guppies, who are currently in QT, I sprinkle a few flakes on top and eventually they notice. Still perfecting how to feed them, I'll let you know if I come up with a better method.
Your tank sounds good. You could even drop down one or two degrees in temp if you needed to for the other fish. They'll be happy fish.