These are not the profiles you find at the official sites and in the books and magazines, but pure additions based on which we discovered next to them.

Will

Will's sensitivity is not just at an emotional level. She also "feels" the presence of things which are beyond anyone else's perception. It's the same feeling which provides her certainties which others can't understand.
She can talk with animals and electric appliances. Moreover she has given names to some appliances and she can make them work without electricity.
Her obstinacy and her closeness makes her and her mother figthing each other and leave each other misunderstood, even letting them loose each others attention to each other.
And Matt. She loves him, but she doesn't dare to tell him. And because of her uncertainty Will soon becomes jealous when Matt introduces another girl.

Irma

At Irma's much is big: her mouth, her (tasty) appetite, her intuition, her humor, and - in decent words - her hormonal development.
If she thinks it's needed she scolds anyone she hates. Sometimes she's awkward enough to previously betray her and the other Guardians' presence. She talks with consumption and manages to make a funny remark at any situation. She has the gift to communicate with water.
Her position within the group varies. One time she makes idiotic remarks and opposes Cornelia, the other time she stands up for others, including Cornelia. She demands solidarity and justice, probably taken over from her father.
She prefers to avoid him, but Martins sense of humor makes her liking him anyway. Sarcasm against him doesn't have any effect. Apart from that he is the only boy in the series who behaves himself like a man. His dullness doesn't afflict that.

Taranee

She's a peaceful girl who sometimes keeps herself on the background. But once she's mad from anger she's a real fury who you better don't mess with. A fire spitting dragon can't outmatch her! Furtheron she's the most telepathic and empatic one of the rest of the group, next to her gift in controlling fire.
Her friendship with Nigel is always a disputed point between her and her mother, who doesn't believe he really rehabilitated himself.

Cornelia

'Style' is the magic word for this lady. You can see that in every aspect. Being tastefully dressed is already known.
While Irma is strong in jokes Cornelia is a star in practical jokes. When many force isn't needed she uses her magic in a subtle way. And even if she's mad she still manages to put some grace in her magic. It's only a pity she's not always realistic enough.
For the ones who want to know: her ability to magically move objects is called psychokinesis in parapsychology.
Another capability of hers is communicating with plants and trees.
Thanks to the swimming lessons of Irma Cornelia lost her fear of water.

Hay Lin

Hay Lin is the most ordinary girl of the group, though she's after Elyon the second most artistic gifted girl. Many sources say she uses her wings to fly, but that isn't true; they don't move when she gets off the ground. It's the air element which provides her the capability to fly. Anyone else can experience the feeling of freedom as Hay Lin does when flying in the so called "fly dreams".
Just like Will gets her information from animals an appliances and Cornelia receives her information from plants and trees, so Hay lin can receive get information from objects (psychometry). The sound of objects gives her information too.

General

When transformed the five have wings, which are too rudimentary to fly with. Even in the Japanese version in which the wings are larger, they can't use them to fly. They have a different function, namely the same as the wings on Asterix* helmet: they show the individual mood.

During the time the girls discovered new capabilities:

Will can speak with animals.
Cornelia can speak with plants and trees.
Hay Lin can create a local and targeting gravity inversion field, which makes walking across ceilings possible.

Collective powers:
becoming invisible;
teletransportation (learned from Caleb)
And what about the Astral Drops: It seems in Tibet are people who can create such alike.

*The adventures of Asterix the Gaul, published by Dargaud® and Les éditions Albert-René®

From issues #49 and #51 the girl's powers have grown, making more things possible:
Will can produce enormous energy outbursts;
Irma gets visions about the present and the future;
Taranee reads also other people's minds than only those of the Witch team;
Cornelia can heal people's wounds;
Hay Lin can feel the truth in whatever someone else says.