The two Petrono Brothers are denizens of San Pasquale.
They are also a pair of vigilantes. As her fellow citizens will warn her, the Petrono Brothers hold Scarlett responsible for the Assassins' attack on their peaceful mountain village. In fact, they are so angry at Scarlett that they take matters into their own hands, resolving to kill Scarlett themselves. So, they stage an ambush just outside the village (which Scarlett will probably encounter while pursuing the A Friend in Distress or A Favor for The Blacksmith quests.
Of course, their plan is predicated on a belief that a murdered Scarlett will stay dead. The experience will allow Scarlett to get a taste of the afterlife of the Twilight World. One she has rejoined the living, she can either forgive them or take her own revenge on the murderous brothers, depending on whether she feels Honorable or Villainous. (Killing the brothers adds 25 to Scarlett's Experience.)