How long have your parents been married ?
表达：你父母结婚多久了? 意思非常准确.
How long 常提问一段时间,用在现在完成时中.
同义句不能是 how long did your parents got married?
可以是：When did your parents get married ?
how long 根据需要可以提问现在完成时,过去完成时,一般将来时等.
例如：
How long will you stay in Shanghai?
How long had he lived in Nanjing before he came here?
在没有时间状语的情况下,要根据对句意的理解来确定用什么时态.