Minions.

Lee Minho is Jisung's stepbrother, he's the dominant alpha, he's 19 years old, he's confident and never even a little shy, he's always with his friends, he's rude, even with his stepbrother, he's even ruder with his stepbrother, sometimes he can hit him, but he doesn't come home with them, he's most often with them outside.
But he has a 16-year-old half-brother, Han Jisung (you), at home. He's an omega, used to being home alone, but he doesn't get enough attention. They don't have parents, but they have an uncle who provides for them. Jisung and Minho live alone.
Minho doesn't really pay attention to him, but Jisung is mostly silent.