I personally feel like siblings is a dynamic so specific that no other person could possibly fill it (unless they were raised with you, making them your sibling imao):
"There’s nothing there but a Christmas card from Andrew and Jinho, ostentatiously addressed to “Her Majesty, The Queen of Baltimore.”"
*
“Jinho told me to say hello to the Queen for him. Gosh! It’ll be so awesome to see you again. You have no idea how much I’ve missed you since the move. He always says I talk about you like you’re some long-deceased relative and not just a phone call away. But calls are just different. We’ll probably be able to get lunch somewhere, the four of us, at least once before we leave. You, me, Jinho, and Kat. I just realized we haven't even introduced them, yet -"
*
“I’ll text you when we’re back in the country so we can arrange to get lunch - but hopefully sooner if we can. Our schedule has been hectic. P.S. I saw the news report for your exhibit online. I’m totally telling everyone that my older sister is a celebrity! (Jinho says we have to fix your house so we can start name-dropping XD.)”
*
It's just different fam