Gyeong:

He has three older sisters. One moved to England, one moved to America and the last is still in Korea. The last one regularly checks in on Gyeong and Laon to see how they are. Gyeong rarely goes out and Laon is always running around somewhere so it's either up to their parents or his sister to come make sure they're both not dead.

Laon:

Laon is an only child. Saeran didn't really have a love for long but had a child she wasn't ready to take care of so Saeran automatically was like "The hell I'm gonna let this baby go through adoption and possibly get abusive parents". So, Saeran took care of Laon and made sure he was taken care of properly. He doesn't want a repeat. Though, Gyeong and Gyeong's sisters have always been like siblings to Laon instead of cousins.

Jisu:

She did have a older sister but... She kind of ran away. They're not sure if she's alive or dead since she hasn't contacted anyone since her running away thing but Jisu still hopes she's alive.

Eunha:

Eunha has a younger brother. He's a cutie and is Eunha's number one fan besides her father. Her brother and Zen always have fights on who loves Eunha more.

Jeaki:

Areum is literally his only sister. If you don't count Elizabeth III or IV. Yes.... the Elizabeth we all know and love died at some point. T-T

Areum:

Jeaki is the only brother she's ever had. Elizabeth III or IV could count as sisters if she wanted them to.

Iseul:

Haneul was his twin brother but.... y'all already know.

Haneul:

Iseul is his twin brother. Haneul is like "that's still my brother. I'm dead, not nonexistent"