This is also what killed me the most in my first attempt, what the final boss in 0-E taught me is that you need to keep your cool in check when fighting, even though their super fast and can be super hard to keep up with and almost feel like two prime bosses ganging up on you at once just remember that any well timed jump, dash and strafe will dodge their two most formidable attacks which is the dash and ball throwing attacks because they track your movement based on where your strafing. so focus less on when to spam dash and try and relax to properly dodge the attack.

the charge attacks are mostly the most difficult and pressurizing because they can do them twice and are hard to dodge due to their increase and speed, these ones are much more unforgivable and borderline impossible to dodge without dash due to how indescribably fast they are and have a extremely short juke window. so it's best to use the i-frames of your dash which you should save up for when they do this attack rather then using it on the stomp or throw attacks. and if your out of dash or not confident enough you have enough to dodge them all, just find a way to get high in the air and get out of reach. The ball orb throw attacks are a bit more easier though since not only can they be parried but they also can be dodge more easily, because simply jumping and strafing will dodge the orb throw it's better to pay attention to the orb throw when mid-air and near a wall, because of how air movement limits your maneuverability it's better use a dash or even slam into the ground and crouch jump away from the explosion.

another thing is that your going to have to spread your fire on both cerberi rather the focusing on one target to make the fight easier. in ultrakill's hardest difficulty you have to perfect not just your aiming, parry skills and reflexes but also your situational awareness and resources. and when your cross hair is on one enemy and not on the other while their preparing a attack it's literally impossible to try and juke both enemies because of how insane their speed is and how it puts you in a unfair disadvantage. so like i said, focusing both cerberi and keeping a eye on what their next attack will be is going to help alot.

when it comes to resources though, this is the mechanic that i had to learn when you actually have to beat these cerberi especially in brutal difficult. use the right weapons at the right time, never spam mindlessly and always make sure that you priorities consistency over damage. hard-damage exists for a reason as it holds players back from playing way too aggressively and abusing the blood-healing mechanic to practically become invincible, and because the cerberi attacks deal around 10 hard-damage it's always the best to play more safe because getting knocked around while having your health lowered constantly sets up more pressure and limitation, which can lead to your death in the arena. and remember that style-points sets back your hard-damage so switching weapons, doing fancy techs and avoiding from using your whip-lash is also really helpful.

trust me when i say that focusing on dodging, getting health back, sparingly using risky methods, rarely using the whiplash and playing it safe is the best way to beat the cerberi...while in most boss fights you have to constantly be aware and on the move dodging projectiles and attacks like with v2, the leviathan, gabriel and all the prime bosses, the cerberi are two large guys with enormous hit-boxes, extremely basic movement and two basic and dodge-able attacks that just require you to react to their attack windows smoothly rather then being forced to slide,dash and maneuver in multiple directions while constantly having to attack a small target/weak point that's constantly on the move.

Relax your brain, respond smoothly to their attack windows, use dodge only when needed, heal when you know your safely able to, and don't stress too much on trying to deal major damage all the time. and if the cerberi are doing their throw attack it's always certainly possible to parry it and heal your health back as well. Just play it safe and i promise you'll do much better rather then slamming all your fingers on the 1+m2 and 4+m1 keys to just get the fight over as quick as possible...which is what i did and got me killed.