Focus on one at a time, having both Seth and Kaim attack the same target, while Jansen casts magic.
If you bought two Steel Swords from Ninn's Boutique in Numara, Seth and Kaim may finish a target off on their own (they have 300HP), allowing Jansen to hit another one with his magic, giving you a good head start.
Have Jansen stop and use Zephyr if your party members' HP drops below 200; the Cavalries have an attack called Rush that does damage in the high 100s.
They're the larger concern, but the thing is, they're in the back row so you can't get them until you take out some of the soldiers first. If you don't mess up too much with the ring targeting system though, and you land some perfects, the battle should prove to be quite possible.
Current PC Build
CPU - i7 8700K 3.7 GHz (4.7 GHz turbo) 6 cores OC'd to 5.2 GHz with Watercooling (Hydro Series H110i) | MB - Gigabyte Z370 HD3P ATX | Gigabyte GTX 1080ti Gaming OC BLACK 11G (1657 MHz Boost Core / 11010 MHz Memory) | RAM - Corsair DIMM 32GB DDR4, 2400 MHz | PSU - Corsair CX650M (80+ Bronze) 650W | Audio - Asus Essence STX II 7.1 | Monitor - Samsung U28E590D 4K UHD, Freesync, 1 ms, 60 Hz, 28"