Cleaning the tombs and paying respect to the dead with offerings（主语）// are（系动词）// the two important practices（表语）// to remember late relatives（修饰表语后置定语）。

参考译文：扫墓和祭祀死者是纪念已故亲属的两个非常重要通常做法。

重点成分解析如下

(1)Cleaning the tombs and paying respect to the dead with offerings为2个并列的动名词短语作句子“主语成分”

(2)are 为系动词

(3)the two important practices为名词短语作句子“表语成分”

(4)to remember late relatives为动词不定式短语作句子“表语practices的后置定语成分”