What branch is grace cahill in

Okay, here's the truth by studying the Cahill family tree of the Oh family and Grace's family. Grace's grandfather Henry was a Madrigal and married another Madrigal: Flora, who had James Cahill, Grace's father. But Flora died and Henry married an Ekat; Hae Oh. They kept the name Oh and had their offspring, Gordan and Bae. Then Gordan had Alistar.
So Grace is a Madrigal and not an Ekat, it's just that James and the Oh twins are half brothers.