Cool I have written a Charmed fanfic too. I am still typing and writing the last chapter up as it has all 4 Charmed ones in it and more characters besides. I have characters and things that I have made up included in my fanfic.
My Charmed fanfic is a little different as I have based it in the Middle Ages or Dark Ages from around the time of Evil Paige. Evil Paige is included in some of my chapters with other things I have made up. She also has a sister and you can probably guess who it is. Then the other two as cousins to Evil Paige and her sister.
They are the Charmed ones of Evil Paiges time. I have made the Charmed ones in two different time eras. I have the 12th Century Charmed ones and the 5th Century Charmed ones which is Evil Paige, her Sister and their cousins.