To resume :

The characters (and and their relatives plus their appearrance if only mentioned)

Part One :

Alpha Gang ;

Nolan Holloway (father and mother) ;

Scott McCall (mother part3, estranged father part4) ;

Malia Hale (estranged father Peter, guardian aunt Talia, older cousin Laura, older cousin out of town Derek part5, older cousin/sister Cora) :

Deucalion (gang composed of : Ennis, Kali, twins Aiden and Ethan)

Part Two :

Hayden Romero (guardian older sister Valerie Clark part3) ;

Marin Morell ;

Gabe (father and mother, little sister with a Down Syndrom) ;

Jackson Whittmore (adoptive father and mother) ;

Josh Diaz (father and mother) ;

Danny Mahealani (father and mother) ;

Vernon Boyd (guardian older sister Alicia) ;

Allison Argent (father Chris, mother Victoria, estranged and unknown grandfather Gerard and aunt Kate part4) ;

Alan Deaton

Part Three :

Corey Bryant (father, mother, big brother, two little brothers) ;

Kira Yukimura (father Ken and mother Noshiko) ;

Lydia Martin (mother Natalie, divorced and estranged father) ;

Erica Reyes (father and mother and Terrier dog Diana) ;

Tracy Stewart (father) ;

Stiles Stilinski (hospitalized mother Claudia and busy father Noah)

Part Four :

Theo Raeken (father and mother Raekens and older sister Tara part4, plus the Alpha gang)

Jordan Parrish ;

Mason Hewitt (father and mother) ;

Isaac Lahey (estranged father and big brother Camden) ;

Liam Dunbar (mother Jenna and step-father David Geyer) ;

Brett Talbot (little sister Lori, guardian Satomi Ito part5) ;

Bobby Finstock

Part Five :

Derek Hale (Hale family plus partner Paige Krasikeva) ;

Mrs Finch (daughter Quinn) ;

Jennifer Blake ;

Adrian Harris ;

Satomi Ito (bunch of people picked up in the street : Carrie Hudson part4, Brett and Lori Talbot part4, high schoolers Jiang part1 and Tierney part4)

Additional characters who didn't have their own P.O.V with further info :

Kylie Tate (father Henri and mother Evelyn), Hayden's friend and a sophomore student (part1)

Matt Daehler, Jackson's ; Danny's and Isaac's friend and lacrosse player (part2)

Kyle, Boyd's friend and in R.O.T.C program and Football team (part2)

Lucas, Corey's ex and a football player (part1)

Harley, Scott's and co's friend (part1)

Danielle, a senior student (part3)

Gwen, a junior student and lacrosse player (part3)

Sydney, a senior student who's held back (part5)

Deputy Strauss, a colleague of Valerie Clark and Jordan Parrish (part3)

Greenberg, a loathed student by coach Finstock (part5)

Mister Garrett Douglas, the physics (AP only) teacher (part5)

Miss Flemming, the calculus (standard and AP) teacher (part5)

Gabriel Valack, an Eichen House patient who had mental illness (part4)

The Dread Doctors, three deranged people who traficked human organs (part4)