Hundreds of fruit flys, how to kill the little buggers!?

Those are not fruit flies they are fungus gnats. You say they are in the plant pots and around the plants. The adults you see flying are laying eggs in the soil and they hatch out often so the adults multiply but if there is no more hatching out they will soon disappear. The eggs hatch into larvae that feed on debris in the soil and plant roots. Mix up some dish soap--about 1/2 teaspoon in a quart of water and water the plants with it That will kill the eggs and larvae. Put some in a spray bottle and spray it at the adults and it will kill them too