I bring character info from X/Y. Sorry it isn't much, but hopefully it will help you understand the main characters a bit better.

Shauna - has a deep desire to travel and have an adventure with Pokemon. She is very determined, courageous, and somewhat loudmouthed. Her main Pokemon is Gothitelle. Plays a role similar to Bianca.

Tierno - A gentle giant, who, in addition to having a passion for dance, also has a strong passion for his Pokemon. He teaches you the basics of Mon Amie, and his signature Mon is Vanillite.

Trevor - Very focused and wise beyond his years, but somewhat patronizing. Extremely knowledgable on Pokemon and the Kalos region. His signature Pokemon is Ralts.