Help with a story

(Warning!! The following post is a bit lengthy, and contains some references to Greek mythology. If you notice any errors in the information I have noted in regards to the myths, please notify me, either here or in PM, whichever you prefer. There are also some references of violence and partial nudity that may not be suitable for some people, but there is nothing horrible graphic or descriptive.)

I couldn't think of where to put this. I didn't think help & advice would be appropriate, because it's not really all that important. >.< I didn't think chit chat would work well either, but I'll leave the mods to decide where this belongs.

I'm working on a story (well, quite a few of them, but one thing at a time...) which is strongly influenced by Greek mythology. Most of the changes I've made so far are to the main characters, and they are fairly easily noticeable, and usually there are several drastic changes per character. But that's just me trying to make the characters my own, and using my imagination.

Characters (Skip this if you want, it's not all that important)

The main character in my story is Pandora. At the beginning, she is made out of clay by a man who challenges the Gods' power of creation. However, when she emerges from the fire, she is cold and soulless and kills him instantly. She reaches out a hand to touch a stone vase, which turns into a golden urn (thus signifying "Pandora's jar" [jar being the actual translation for the word used in historical texts, not box]) and holds the powers of death, age, sickness etcetera that are unleashed by Pandora in the myth, though I've read that in some versions the only thing it contains as a gift of hope, which I'm not sure how that works. Nor am I sure how a jar can be opened, but oh well.

Anyway, the other main characters are;
Fury
In mythology: Furies were clawed, winged creatures that drove men mad with their own sins, particularly those who had killed a family member.
In my story: Has the appearance of a young teenage woman with grey-purple skin and yellow eyes. She has sharp teeth and long claws that can cut through steel and bone easily. She has one blue bat wing and one red one. Blood red feathers cover her chest and she wears a grey cloth around her waist but is otherwise unclothed. She keeps seven fierce pets inside her (one for each of the deadly sins), and she draws power from the sins of man of which she feeds on.

Madea
In mythology: Madea was a witch, who fell in love with a hero and helped him to retrieve the golden fleece. When fleeing from her father, she chopped up her brother and threw him overboard knowing that her father would stop to retrieve his son. Appalled by her actions, the hero abandoned her. There's more to Madea, but I can't remember at the moment.
In my story: Has the appearance of a tall woman with hair of red and eyes of green. She wears a long, flowing, dark purple, velvet cape and floats above the ground. She wears emeralds around her neck and ruby earrings. She is wicked and spiteful, and she casts dark and twisted spells. She carries with her the book of the dead which grants her powers over spirits and the dead, and gives her the dark powers she possesses. The book can not be taken from her, nor can it be destroyed as it was made by the beings of the underworld.

Namean
In mythology: One of the tasks of Herecles was to kill the Namean lion, a giant monster with a hide that could not be pierced by any weapon, resulting in the hero strangling it with his bare hands and wearing the hide as protection.
In my story: She is a giant of a woman with gold hair that is striped black and brown. Her skin is golden brown and also striped black and sandy brown. She has hollow orange eyes with no pupils and serrated, crooked fangs. She has amazing strength but in addition her skin can not be pierced by any weapon. She has curved claws on her hands and two great horns, and is not clothed, although her “fur” prevents her from being revealed. She’s not incredibly intelligent, and doesn’t speak much but she is quick to anger, and her roar can crack stone. She carries two massive swords that are said to be carved from the bones of a titan.

Adonis
In mythology: As far as I know, Adonis was a very minor mythological character, who angered Athena (I believe, or some other goddess) and was gored by a bull. In mythology, he had no direct connection to the character I have listed as his alter ego, I just like the name Adonis. Charon was the rowman of the river Styx, and was not portrayed of a monster of any sort, to the best of my knowledge, which admittedly is a bit rusty.
In my story: A tall man clothed in black with a white mask on his face. The mask has yellow eyes and purple swirl patterns and has a frightening smile. He wears white gloves and doesn’t speak other than to hiss like a snake and growl like a dog. His hands control the flow of time and he keeps within him a demonic alter ego named Charon. Charon is a large man with rotted flesh and hollow silver eyes that can reach into a person’s body with his bare hands. Broken chains dangle from his wrists and he carries a scythe.

Echo
In mythology: Echo was a Nymph, who betrayed her promise to a goddess (forget which one, perhaps Hera) and fell in love with a man. As punishment, she was condemned to follow him, never to be seen, only to echo the final words of his sentences.
In my story: She is the ghostly figure of a beautiful woman. She has flowing silver hair and sad blue eyes, but deep down she carries frightening menace. She silently stalks men and reaps their despair to grow power and often drives them insane with her whisperings, leading them to kill themselves. She wears a long, slender, and flowing grey dress. If a man looks upon her ghostly figure, he is immobilized as she taunts and seduces him before ripping him apart. She has the power to pull objects of torment from the air, and become solid or ghost at will.

Story (This is where the problem is)
As I have it right now, the six characters are a wide variety of species, with abilities derived from various magical items or deep hatred or other such feelings, but at their roots their are mortals. They have been presented with a task by the Gods to punish people for their sins. The problem is, I love the beasts of mythology and want to incorporate them into my story, and have my characters fight them. But if they are punishing people for their sins, it doesn't make all that much sense for them to be killing off monsters does it?
I had the idea that maybe they could be charged with killing the previous beings of chaos and destruction to gain immortality, but something about that just doesn't fit for me. I was wondering if anyone could offer some suggestions?

I apologize, this was horribly long. But I really love Greek mythology and am really liking the idea for this story (though, I haven't figured out exactly how Pandora comes to meet the other five characters yet) but I can't even come up with a central plot point yet. And I wanted people to be informed of the feel for my story and such. So yes. Thank you for your time, and again, I'm sorry. ^_^; (*hug*)