Did a bit of reading, and found my error - Gehn's wife is only seen in a picture in Riven, so I assumed that she was Rivenese.
According to RAWA, she's human. (Weird, when you think about it - wouldn't have pegged Gehn to deal with hoo-mans.)
So, the progression is
Aitrus (D'ni) marries T'iana (Human), they beget Gehn (1/2 D'ni, 1/2 Human)
Gehn marries Keta (human), and beget Atrus (1/4 D'ni, 3/4 Human)
Atrus marries Catherine (Rivenese) and beget the boys and Yeesha (1/8 D'ni, 3/8 Human, 4/8 Rivenese)
Yeesha and a D'ni would have kids that are 9/16 D'ni, 3/16 Human, and 4/16 Rivenese
*checks his fractions, and nods*
D'ni father, half-Rivenese mother, Rivenese grandmother, human great-grandmother. I'd still call The Child D'ni / Rivenese, myself.
This post has been edited by Crazyfox: 15 November 2007 - 05:20 AM