I see a lot of things wrong with your story, such as wrong names used for the boys, since all the y/n characters are above 16, they shouldn't be called oppa- along with that Koreans don't we like being called oppa.
You sexualize minors. I already see you've taken down one of your stories that contained it but if any of the others do you need to delete them too. It's just not okay.
If you want to use something proper,use 小弟弟 , or Didi
It means little brother. Please for everyone's sake do not sexualize minors.
