【上下同门】〖shàng xià tóng mén〗[up down together door]

上辈姑嫁叔，

下代姪侄婿。

同家两岳丈，

门当户对娶。

姑婿与侄婿的互称。上下：指上一辈与下一辈。Aunt husband and niece husband of mutual call. Upper lower: refers to previous generation and next generation.