The Idaho Supreme Court ruled Wednesday that two orphaned children will remain with their grandmother in Argentina, not with family members in California who also wanted custody.

The ruling means that Alden and Aliana Heiss will stay with Violeta Conti in Ushuaia, a region dubbed "the end of the world" by locals.

The children's parents, Karl Heiss and Marisa Bauducco-Heiss, were killed in a car crash near Seattle last year. Aliana, who was 10 at the time of the crash, sustained severe brain damage in the crash; Alden, who was 6, suffered whiplash but has fully recovered.

The parents had handwritten wills granting custody to Conti, but paternal grandparents Fred and Anna Belle Heiss, of Malibu, California, sought custody. They contended Aliana needed medical care only available in the U.S. and that Alden would heal better from the emotional trauma if he was in a familiar setting.

In the 14-page unanimous ruling, Chief Justice Daniel Eismann said state law, which places the deceased parents' wishes first when determining guardianship, doesn't jibe with the Heisses' contention that the best interests of the children should be the primary factor in determining custody.

"It is the legislature that has the power to change the statutes, not this Court," Eismann wrote. "The legislature obviously believed that parents should be able to direct who will have guardianship of their unmarried minor children in the event of the parents' deaths."

Eismann said the father, Karl Heiss, was "empowered" to choose his wife's mother as the children's guardian under state law.

Besides upholding the parents' choice of Conti as guardian, the high court also overturned a lower court ruling that made the Heisses co-guardians while the children visit for one month of the year.

That arrangement could cause more problems than it solved, Eismann wrote, and instead Conti could give the Heisses a limited power of attorney so they could handle any emergency medical care, international travel arrangements or other details during visitation.