Your tank is a 15-16 gallon tank. In my opinion, you are overstocked with mid-top level swimmers. You also have livebearers and if you don't have all males, you will be inundated with fry.
Corys should be kept in groups of 3, absolute minimum, or more. 5 is best. Yes, you have to feed them. They are scavengers but would only profit from you overfeeding the tank unless fed separately.
Fish only school when threatened by a predator, it's not a natural instinct in a home aquarium.
75: blood parrots, featherfin cat, emperor tetras, turquoise rainbowfish, BN plecos, japanese trapdoor; 46: WCMM, gold inca snails, ghost, bamboo & amano shrimp, kuhli loaches, rummynose & ember tetras, endlers, platies, flame gourami, guppies; 16: pygmy, peppered, loxozonus corys, otos, assassins, RCS ... ~ Research PRIOR to purchase.... ~