Who is Inchun, Sookan's Little Brother from Year of Impossible Goodbyes and what is their importance?

Inchun is Sookan's little brother, the youngest of six children. He is only six or seven years old, but he often seems more like an old man, giving Sookan wise advice for how to succeed socially. He remembers from stories how important it is to never speak Korean at school. Inchun is even better behaved than Sookan, and since he can not use real drawing supplies, he likes to use a stick to draw in the dirt of their yard.