Oliver who

Oliver is a serious, hard-working, and intelligent math prodigy, even tutoring his senior students in math that is above their grade level. At first, he is portrayed as aloof and closed off, but he slowly warms up to people and reveals a deep personality. He is not very expressive with his facial expression or body language, but can be kind and considerate when it comes to the people close to him, even opening up about his dysfunctional home life and that he is saving up money to buy a new guitar, a replica of the one his stepfather David sold to a pawn shop and never got back.

Joanne: Oliver's relationship with his mother is strained after her new boyfriend/fiancé David sells Oliver's guitar, an incident that leads to him moving in with his stepfather Auther Yang, he has said that he loves his mother but refuses to move back in with them because of David.
David - David is Oliver's stepfather. Meg claims that David isn't such a bad person, but Oliver refuses to give him a chance because he sold Oliver's abandoned father's guitar to a pawnshop and decides to move out before Joanne and David's wedding. However, Joe has stated that everything was fine and that the siblings were supportive of their relationship, suggesting that Oliver was okay with him at one point.
Joe Yang - Joe is Oliver's older brother. They have a very close relationship, as can be seen when Oliver decides to live with Joe and Joe's father instead of at his mother's house. Joe adores Oliver and always makes sure he is okay.
Meg Yang [1] : Meg is Oliver's sister. Not much is known about their relationship.