Delayed Blast Fireball has a unique clause about physically grabbing and throwing the spell itself: If the glowing bead is touched before the interval has expired, the creature touching it must make a Dexterity saving throw. On a failed save, the spell ends immediately, causing the bead to erupt in flame.
Damage one Hand first and when they are stunned, use this time to focus on the other boss. Deal damage to them, rinse and repeat. Each boss gets stunned twice (once towards the middle of their health bar, and once towards the end), so staggering which Hand you attack maximizes time fighting a Hand solo.