In your case, you seem to say that to k-popstar. If it's right, '오빠는 춤을 잘 춰요.' is much better. Korean guys loves to hear the nickname '오빠'. It doesn't matter they are biological brothers or not. Even grandpa will be happy to be heard it. lol
I saw lots of korean learners using '당신' in this site. Don't try to use the word'.
We don't use '당신' in conversation often.
You can see the word '당신' in music lyrics or novel books, formal docs, when people fight. ex) 당신이 뭔데! or the name of senior people.
mom was upset at mom-in-law. mom is explaining to dad what grandma did to mom.
dad: 어머님이 왜 화나셨어? (how come mom is upset?)
mom : 당신이 먼저 화를 내셨어. (She was upset at me first).
we don't say 그녀가 먼저 화를 내셨어.
I hope this is clarified using '당신'.