Summon Shelldon behind or to the side of the boss and away from the spirits. This will keep the heat off of the spirits. Stand close enough to Shelldon and the spirits so that your area healing will reach them.

Unstable lazer is better than unstable beam for this because the bees and shelldon (and you) will trigger the lazer far more often than just you triggering the beam. The beam does about 66% more damage, but the other attacking pets that can trigger the lazer make it the better option.