彼の妹は

his younger sister

→ 彼
phrase Rare #33,903
his younger sister は marks his younger sister as the topic of the sentence.
JA: 彼の妹は大学生です。
EN: His younger sister is a college student.

彼の妹はとてもかわいいね。

His younger sister is so cute.

彼の妹は二人とも美人です。

Both of his younger sisters are beautiful.

ジョンと言えば、彼の妹はどうなったかな。

Speaking of John, I wonder what happened to his sister.

彼の妹は流行を重視し過ぎる。

His younger sister cares too much about fashion trends.

彼の妹はアメリカにいきません。

His younger sister isn't going to America.

彼の妹は人気のテレビタレントだよ。

His younger sister is a popular TV personality.