While translating a book on the aboriginal people of northwest India, I came across a tradition of marriages, where one brother–sister pair were married to another brother–sister pair, as well as many similar traditions.
They have a word for this kind of marriages in my native language, so I was wondering whether English has such a word, too. Does it?
In English, the preferred term appears to be double in-law marriage. The two couples become double in-laws or simply double couples.
From Adverbial Subordination in English: A Functional Approach by María Jesús Pérez Quintero:
... morning, which would bore me), to a complete clause (e.g. Things then improved, which surprises me) or even to a series of clauses (e.g. Colin married my sister and I married his brother, which makes Colin and me double in-laws).
From Family Faith Stories by Ann Weems:
John's sister was married to Mary's brother, which made them double in-laws. John's sister died, probably of some fever because then, before 1860, John Griffin, who was also a doctor in the Cokesbury district, died, leaving two young boys.
From Thicker Than Water: Siblings and Their Relations, 1780-1920 by Leonore Davidoff:
Sisters and brothers married each other's brothers and sisters, becoming double in-laws. Such 'close marriages' doubled or trebled the kinship ties between their respective families (see Chapter 9). In the short run such doubling potentially ...
TV Tropes too has a page on double in-law marriages:
Bob and Janet are siblings. So are Spencer and Alice. Alice marries Bob, while Janet falls in love with Spencer. This would also work if Alice and Janet were sisters, and Bob and Spencer were brothers. Then Alice would marry one brother, and Janet would marry the other. In other words, a pair of siblings marry another pair of siblings. Someone marries the sibling of their own sibling's spouse.
Language equivalents exist only if cultural equivalents exist. This is a phenomenon that seems prevalent in Indian culture; not so much in others'. There is no equivalent in the English language.
Two words and a historical note, none of which definitively answer the OP's question.
A term which is perhaps broader than you desire is Endogamy, or marriage within a specific group. However, this does not restrict the marriage to brother/sister pairs.
A Sororate marriage refers to one man marrying a woman and her sister, usually after the woman has died or is proven infertile. (It may be helpful to peruse this list of Types of Marriages.)
On a side note, the eponymous Siamese Twins, Chang and Eng Bunker, married sisters Adelaide Yates and Sarah Anne Yates. They were married in a single ceremony on April 13, 1843. They had 21 children in this marriage-type-without-a-name. Their children were double first cousins.
