Those who played the Original Hyperdimension Neptunia game, would have figured out or learned, that the CPU's are in fact sister in that game only.
All were created from the power and traits of Arfoire, they all share Arfoire's traits and maybe DNA to. Thus making them sisters.
Vert makes this statement in the True Ending of the First Games, so if you don't belive youcan always cehck out the true ending.
So here are the CPUs living in normal everyday lives as sisters.