The Knights win. Misaki and Haku aren't even needed.
Irene's blasts in her human form barely do any damage and can be dodged by Alvarez-arc Erza. This version of Erza could also land shots on her.
We have Suzaku taking down a superior version Erza and base Natsu in one hit, and Kirin beating up Laxus (pre-LDK), who's on the same level as Erza.
She's already at a massive disadvantage due to them being dragon slayers: we've seen that DF Wendy could hurt her human form and Erza taking down her dragon form in one hit with her Benizakura sword enchanted with dragon slaying magic. Overall, they should deal with her quite easily.
Now August. He can copy Suzaku and Kirin's magic but cannot replicate Suzaku's sword nor negate the damage from it. Given that he took down Erza and Natsu in one hit, he must be able to critically injure August at the very least with his strongest attack. Kirin can throw him around with his coffin and hit him with lighting blasts too.
To August/Irene supporters: the DDSK being Gildarts-level in magic power doesn't mean they share the exact same stats as him. Especially talking about attack power, speed and durability. And Irene using Wendy's power to pin Haku down with his plushies doesn't translate at all about how she will do against Suzaku and Kirin as they do not share Haku's stats.