(I used Gacha Club to make the characters looks)

Alistair Omega
Age: 21
Human form:

Demon Form:

Sam Williams (Sammy)
Age: 18

Simon Williams (Sammy's twin brother)
Age: 18

Mara Omega (Alistair's sister)
Age: 18
Human form:

Demon form:

Becca Woods ( Sammy and Simon's cousin. Mara's best friend)
Age: 18

Zac Omega (Alistair half brother)
Age: 20
Human form:

Demon form: