Charlotte is the first of the Warren line. Charlotte was a part of a colonial witches coven that acknowledged the power that her daughter, Melinda Warren, would possess. At the time she was in labor, a woman who wished to have Melinda's power for herself kidnapped her, but The Charmed Ones of the future were transported back in time to save her. The three sisters are descendants of Melinda and Charlotte, and Piper helped to bring Melinda into the world. She would later name her first daughter after her favorite ancestor, Melinda.
Melinda is the daughter of Charlotte, and grew up in the 17th century in Salem. There isn't a lot of information about her, but we do know that she had a lover named Matthew Tate, a warlock who betrayed her by revealing to the town that she was a witch. They burned her at the stake, even though she could have used her powers to save her own life, so that her daughter might be saved. She returned centuries later to help the Charmed Ones defeat Matthew Tate.
Prudence is Melinda's daughter, who was raised as an orphan after her mother died. The Warren line was carried on through her, and she is the ancestor after whom Prue was named.
Brianna is an ancestor of the Charmed Ones who had powers resembling Prue's, but magnified many times over. She disgraced Gabriel, the Lord of War, during the premium war by using her power to strip him of his sword, throwing it a hundred miles away. Centuries later, he came back to try to regain his powers by attacking Prue.
(The Charmed Ones' Past Lives)
Although Prue, Piper, and Phoebe lived in the manor during the roaring '20's, they were not the tight-knit sisters we see presently. They were cousin witches, with powers very different from their current powers. Phoebe was turned evil by a shapeshifting warlock, convincing her to use her powers against her cousins so he could become more powerful. The past cousins put a curse on past Phoebe so that she would die on the same day in all her future lives, but the Charmed Ones skipped around in time in order to protect the good Phoebe from dying. This explains why Phoebe's power is an inactive one, since if a power is misused, a witch may regress and lose her abilities in present and future lives.
Penny "Grams" Halliwell
Penny is the grandmother of the Charmed Ones, sort of a surrogate parent after their father left and their mother, Patty, was killed by a demon. Penny was a powerful witch who died of a heart attack when the girls were in their twenties. After she died, their powers that were bound were made known to them, and the sisters officially became the Charmed Ones.
Patty Halliwell is the mother of the Charmed Ones, and a witch herself. She was killed when Prue was around 5 or 6 years old, Piper was 3 or 4, and Phoebe was just 2, by a water demon. She had been divorced from her husband and the sisters' father, Victor Bennett for some time, and had taken up a relationship with her whitelighter, Sam. Their love produced a fourth sister, which the true Charmed Ones had no idea about, since Patty and Sam gave her up for adoption right after she was born.
Prue, Piper, and Phoebe Halliwell
These sisters are the original Charmed Ones, and like all normal people, they have jobs, hobbies, guy troubles, and they struggle to lead normal lives. With demons dropping in all the time and each of them facing a the challenge of figuring out a new power, it can often be difficult. When Prue, the eldest sister, is killed by a demon at the end of season three, their spirit of a mother reveals the existence of a fourth sister, and the chance to reconstitute the Charmed Ones, which brings us to...
Piper, Phoebe, and Paige Halliwell
The newest sister isn't the only one who has problems with the idea of being a witch. After the death of her sister, Piper wasn't even sure she wanted her powers anymore, let alone another sister who would bring the Charmed Ones back from the dead, so to speak. It will take a while, but the Charmed Ones will be just as powerful as before as soon as they can find it in their hearts to accept each other.
(Most copied from Charmed Fans Online)