When you sneak attack with one of the orb or lesser orb
spells from Tome and Blood, do you get sneak attack
damage from every orb in the volley? Also, what effect, if
any, does the Fortitude half saving throw have on the
sneak attack damage?
  The sneak attack damage applies only to the first orb in the
volley, just as it does when you throw multiple shuriken as
part of a single attack action. If the first orb hits, add the
sneak attack damage to the orb damage, then roll the save,
and halve the result if the save succeeds.