Head into the arena and start building Focus Points right away since theyll be your main advantage here. The Focus Gauge fills up pretty quick if you mix Light attacks with Staff Spins, and you might want to spend some Spark points in Staff Stances to get more Focus Points capacity. Try keeping both bosses in view, and use those pillars around the arena to break their line of sight when needed its actually pretty helpful.

Something interesting about Spirits, you can grab them from certain enemies you beat and store them in your upgraded Gourd to deal serious damage later. Keep an eye on the bottom right of your screen for the Spirit gauge, and make sure to watch for any Spirits that show up in the arena during the fight. Switching stances is really important here, use Quick stance when you need to move between bosses, then Heavy stance whenever you spot a good opening to attack.

Maybe worth noting that you can actually use one boss to build your Focus while dealing with the other one dodge their attacks to fill up the gauge, then unleash everything on your main target. Watch out for those arena hazards though, they can mess you up pretty quick but sometimes you can trick the bosses into them which works great. Stick to short combos like one or two hits unless youre absolutely sure its safe, and remember that perfect dodges give you a bit of Focus too which is pretty nice. Just take your time with it, and youll start seeing more chances to deal damage as you get comfortable with their patterns