These two unnamed twin sisters were two people Bobby Singer failed to save during a hunt.
At his home, Bobby is confronted by the spirits of these two young girls, who accuse him of failing to save them from the 'monster' that killed them. They capture him and hold him in a wrecked car in his salvage yard while they torment him. Sam Winchester managed to find and rescue Bobby. Bobby leads Sam and Dean Winchester to a safe room in his house.
Bobby found a spell to put the spirits to rest and they left the safe room to prepare the spell. The boys gathered all the supplies for the spell and Bobby with Dean's help complete the spell and the spirits vanished.
- The ghost twins are likely a reference to the urban legand of ghost twin girls that show up and ask people if they want to play with them. It may also be a reference to the twins from the film 1980, The Shining.