他们真厉害用英文怎么说

"They're really good" 或者 "They're really skilled" 都可以用来形容某人真正地厉害。

例句：

"They're really good at basketball." (他们篮球打得真好。)
"They're really skilled at playing the piano." (他们弹钢琴打得真厉害。)

来源：这个表达是经典的英语表达方式，在英语中广泛使用。