The Native American symbol for sisters depicts two women standing side by side with a line connecting them, surrounded by a circle. This represents unity and equality resulting in a never-ending bond.
Many Native American tribes in the 1800s engaged in the marital practice of co-wives, by which a man married more than one woman. In many instances, the co-wives were also sisters because the tribes believed that siblings were more agreeable with one another. If an oldest daughter had multiple sisters, she would marry first, and then her sisters would marry the same man as they came of age.
The symbol for brothers is exactly the same as the symbol for sisters except that it depicts two men.