关于Killers的意思和用法的提问

Q: When the Killers performed on Tuesday night at the Theater at Madison Square Garden, they were a band caught between two personas that might be described as high-school and sophomoric: self-mocking versus earnest, self-obsessed versus lofty. 是什么意思？

Q: I'd appreciate if you could correct my English!

I watched 'Killers of the flower moon'.
Leonard DiCaprio is staring on this.
This has made based on the true incident that had happened about 100 years ago in the US.
It's the story of horrible murders that many native Americans, called Osage people, were killed by white people who want Osage's oil money.

「キラーズオブザフラワームーン」を見た。
レオナルドディカプリオ主演だ。
100年前にアメリカで実際に起きた事件が元となっている映画である。
これは、オーセージ族というネイティブアメリカンの人たちが、彼らのオイルマネーを狙う白人たちに次々と殺されていくという残忍な事件のお話である。

Q: I was listening a The Killers song's called "when you were young". There was a part that i can't understand, because i think that's a idiomatic expression. So, what does "sit there in your heartache" means?