Sisters, maybe twins, possibly cousins. We won't know unless we see their birth certificates, the real ones, not the ones they use to get ID.
This is what they do for a living. They walk in, take what they need, walk out again.
It's not glamorous. It's just business. It may not always be strictly legal. It's just business.
They are too smart for this, and too tired.
They share clothes, wigs, makeup, cigarettes. Restless and hunting, they move on. Two minds. One heart.
Sometimes they even finish each other's -
From Neil Gaiman's short story "Strange Little Girls"