语法没错
分析句子结构,what concern you and other teachers 是宾语从句(稍后用*代替), we know * are the unhealthy websites. 因为websites是负数,所以谓语用are.
但这是典型的中文思路翻译出来的英文,真正的英文表述是这样的：
we know that the unhealthy websites are you and other teachers' main concern
或者
we know that the unhealthy websites are the main concern of you and other teachers