How is paige sisters to the charmed ones?

The Paige Matthews is NOT a sister to the Halliwell sisters (Prue, Piper, and Phoebe) in the TV show "Charmed."

Here's the breakdown:

* Prue, Piper, and Phoebe Halliwell are biological sisters, the Charmed Ones.

* Paige Matthews is their half-sister, the daughter of their mother, Patty Halliwell, and her Whitelighter (angel) lover, Sam Wilder.

* Paige becomes the fourth Charmed One after Prue's death in season 3.

So, Paige is not a full sister to the Halliwell sisters, but she is their half-sister and becomes a powerful witch and the fourth Charmed One.