To break the famous spartan phalanx formation, use heavy attacks and attack them while they're in disarray or after they pounce with their spears. Keep doing this until Megaera appears. You have to prioritize dealing damage with her since the supply of soldiers will be infinite. You'll have a brief warning of her attacks; just take note when her claws are glowing then move out of the way.
Once enough damage is dealt, she'll climb the roofs and start attacking you with projectiles and exploding bugs. Kill the illusionary soldiers then pick up their spear. Use it to damage the fury until she falls down to the ground where you can deal massive damage to her via QTE.
During the scene, you'll be pinned to the wall by the fury's familiar. Attack it and evade as necessary to complete the short mini-game. You'll have to fight Alecto afterward. When she's raining fireballs is a good chance to attack her. Just land a few light hits then evade as necessary. Be careful of her charges as well. Keep doing this until she is weakened. Grapple her to start a QTE.
Magaera will join the battle this time. You have to keep watch when they're bracing for an attack. Observing and reacting to their charges will help in this battle a lot. One thing you can anticipate is Magaeara's air stomp that releases an area-wide shockwave. The screen slows down a bit before she triggers it so you can time your jump and avoid damage. After doing her stomp, she'll usually be weakened and vulnerable for a few seconds. Use this chance to deal damage to her.
Once enough damage is dealt, she'll surround herself with a protective barrier. Don't bother attacking her anymore. Focus on her sister and attack her while she's lobbing fireballs around. Be careful since Magaera can still use her claws to create a small shockwave upon impact. When they're both weakened, grapple them and complete the QTE to complete this chapter.
Battle against two sisters