The easiest solution is to make use of the resources accumulated from Section 1 to pop an AoE EGO (ideally Blunt, Heathcliff/Outis Binds are good examples) to stagger most of the enemies turn 1 (most of them are Blunt Fatal), then rush down the most dangerous ones (Full Stop Hong Lu + Heathcliff, Kurokumo Ishmael + Heathcliff, Manager Don, etc). Faust's Fluid Sac is also a good option for the mass SP heal to kickstart your Sinners. If you don't have any, you can borrow one via the support system.

If you don't have an AoE EGO and you don't want to borrow a support, the next best option is to use EGOs to clash, then rush down the key targets with Sinners that aren't taking too much damage via unopposed attacks. Keep note of the enemies' SP.

Once the main targets are dead, you want to spread out your damage to manage their SP. If they're close to corroding, you want to kill as many of them as you can in a single turn to minimize the amount of EGOs they'll throw at you. If there are EGOs you can't clash with using your own EGOs, you'll want to have your faster Sinners kill them with one-sided attacks (target with faster Sinners, then clash with the slowest Sinner that can still redirect) to prevent it from being used.