polyamory

A form of relationship involving more than two people. The relationships may be symmetrical (like a triangle), or something more complex. The relationships may also be open or closed, straight or gay, or a mixture. A purely heterosexual form of polyamorous marriage was once practiced among the Tibetans: each man had many wives, and each woman had many husbands. This raises the possible of your brother also being your husband-in-law-in-law.