There are 4 Coeurls at the start of the fight, 2 on each side. Each Coeurl when defeated will spawn anothe Coeurl somewhere on the map, so there are a total of 8 Coeurls. They all have the same stats and abilities.
The Coeurls have a move that can inflict area-wide paralysis and deals damage, and also a single target silence ability. Units with low faith may have an advantage here. You'll want to have a tank and lure the enemies away from the party to avoid getting group paralyzed.
They also have a 2 hit attack, which can be dangerous if they group chain it. It's a lightning slash type attack, so you can build up some resistance by using VCs or skills like Double Resist.
If you want to lower their numbers, focus on the one the reinforcements one at a time.
Earth units can help make it easier to deal damage because of the elemental advantage. Being able to one-shot them will make the whole fight a lot smoother. Malboro and Tonberry have paralyze resistance in their skill boards if you really need it.
When it comes to damage, most damage dealers will work just fine once you have a proper tank. There are plenty of cheap or free to play options available.
Zazan and Siren or Iron Giant espers have beast killers, for easy one-shot potentials. Sylma and 9S are units available to all players during Coeurls release. Tidus can still work as well, but there is an elemental disadvantage.