Cha Hakyeon (Name of seer: N)
Seer
Eyes and hair colour subjected to changes when using various abilities. 

Ability:

• Sees the colour of people's souls to know exactly what they are
• ability to look into someone's past just looking into the person's eyes (these visions come randomly, as in no chronological order. At first glance it could show you the memory of the person as a baby and the next time you meet the same person, it could be a vision of how that person dies)
• can absorb the pain and sadness of how one is feeling (in order to cheer someone up, he will take the pain from you).
• may have random visions of the future

Awakened abilities:

• displays elemental abilities

Jung Taekwoon (Name of necromancer:Leo)
Necromancer (magic and foresight usually related to the darker side) 
hair is usually dark, eyes as well.

Abilities:

• able to see into the future only if something bad is going to happen or when in contact with something or someone and chooses to see.
• ability to enter people's nightmares or inflict nightmares…often does it unknowingly or in sleep.
• ability to self heal 

Awakened abilities:

• The ability to summon souls
• communicate with the underworld
• blood bending. (blood bending meaning he can shape blood into shapes and weapons, this often means he needs to hurt himself to extract blood but he can self heal.)

Lee Jaehwan (Name of fairy:Ken)
Fairy
Hair may turn blonde when he uses too much ability.
Eyes are green in fairy form

Abilities:

• Make people feel better, happier just by being near the person
• ability to shrink and fly around, this is known as fairy form (only can fly when shrunk)
• green fingers (revive dying plants when he touches them)
• can make wounds smaller but not heal them completely (drains a lot of his energy)

Awakened abilities:

• Plant manipulation
• Plant detection (plant detection means if he is in a certain area, e.g. his house, and someone steps on the grass in the backyard he will know)

Kim Wonshik (Name of demon: Ravi)
Incubus
Ability to change his hair and iris however he likes to make himself look more attractive
When hungry or feeding, iris turns red

Abilities:

• to make people do what he wants them to do just by making eye contact
• able to seduce people with the snap of his finger..only if he wants to
• thought manipulation
• absorbs energy from both humans and creatures 

Awakened abilities:

• Shadow manipulation
• Invisibility cloak
• Pain infliction (through thought manipulation)

Lee Hongbin (Name of siren:Kong)
Siren

Ability:

• Able to control people using his voice (can incite the person to die, but unable to make the person kill themselves directly)
• can enter one's mind and mess it up by looking directly into someone's eyes

Awakened abilities:

• heightened agility
• ability to predict the future movements of the opponents

Han Sanghyuk (Name of shapeshifter: Hyuk)
Shapeshifter
When in animal form one iris will be hazel and the other will be blue

Ability:

• Able to change into anything he has previously come into contact with using his memory
• can subject the changes to only specific parts of his body (he can be fully human with only a right cat paw)
• can be inanimate objects
• can look into the past of any object

Awakened abilities:

• Cloning (can only recreate 2 more of himself, knowing how much of a naruto fan he is I couldn't help it.. )
• ability to communicate and summon animals

Aurora (Name of seer: Ro)
Seer

Abilities:
Not yet known

Awakened abilities:
Have yet been awaken

Minors:

Xylo (the brother)

Werewolf

Fey (the sister)

Dryad (Tree Nymph)

Mother

Angel

Father

Merman

Explanation (will be updated as the story progresses):
The reason why they all have voices in their heads is because these magical creatures coexist with the host. The host is the human body and human brain, that's why it often seems like 2 people are having conversations during these chapters. The closest reference I can find is the jinchurikki in naruto, but these mythical creatures are more amiable and doesn't mind being in the bodies of these hosts and coexisting. Except for Ravi and Wonshik...for now..maybe? I won't spoil it.

Cursed creatures are creatures that are requires to survive off of something, such as vampires and incubus.

Also tried to colour code the creatures to give you a better idea of how they look.

Parents of creatures know the creatures before their child is born as the creatures will ask for permission to coexist with their child.