This is aptly recognised in the Hindu Succession Act also, as the wife's relatives do not have any claim. The so-called "inlaws" are practically "outlaws"to as far as the law is concerned.
Even in the western milieu, right from Sophocles' "Antigone", who rated a brother's love higher than a husband's or even children's, to Eliot's Tom & Maggie, who were not separated even in death, in "The Mill on the Floss", sibling love is celebrated. Even in later times, the Lamb siblings, Charles & Mary lived a full literary life together. In "Anne of Green Gables", Matthew & Marilla spent their whole life contentedly, with the irrepressible Anne for company. Even Harry Potter, despite extreme closeness to Hermione, was unable to think of her as anything other than a beloved sister.
Of course, India is the only country, where "Rakshabandhan", celebrating sibling love, is a national festival. Even Draupadi, in spite of having five valorous husbands, had to depend on her brother Krishna, to save her honour. The spiritual leader Sri Ramakrishna, in his "Gospel" repeatedly exhorts his devotee couples to live as siblings after having a child or two.
To end on a personal note, this writer's father, the eldest son, & an ideal brother was the heir to a prime property in Bangalore. He gave priority to the claims of DNA, rather than marriage, & gave up the whole property to his sister cheerfully, whose descendants are enjoying it happily now!