中翻英一句：「其實，你們都錯了。」感謝。

Actually, you are all wrong.

口氣緩和一點：
Actually, you are all incorrect. (只表示對方回答不正確)

In fact, you are all wrong.
In fact, you are all incorrect.
In fact, none of you is right.
In fact, none of you is correct.

"in fact" 也可以用 "actually" 代替。

In fact, you were wrong.

In fact, you were wrong.