They're fairly weak so just attacking them as normal is good enough against them.
Blitz against them is good since so many of them will be close together. For a professional Ravager like Hope, wide-range spells work well. Aeroga may cost the most ATB segments, but it deals the greatest amount of damage and range effect in its use to a lot of enemies. Use this on the Numidias altogether for easier and quicker defeats. It's even better to fight with characters that all know Aeroga to sweep all the Numidias away at certain intervals.