they have been married for a year.

have been married 表示一种状态
have married 表示一种事实，我已经结婚的，这里的结婚，是一个瞬间的动作，不能与for a year 这种表示状态的短语连用
have been marring 表示一直在结婚
总的来说，marry 是一个表示瞬间的动词

be married (to sb.)是短语。
已结婚两年是现在完成时

married是短暂动词。。不用有延续的。。
所以要加Be
这样就可以当作状态了

they have been married for a year
have been married 表示状态 和后面的for a year(时间段)呼应

They have married.----married是动词

they have been married for a year.---married 是形容词

they have been marring for a year.晕 老大 这句话 是是现在完成进行时!
意思是 过去的一年里他们一直在结婚!

be married 和 get married 是词组 固定的！