From memory of discussions with Bruce
As you say, Shalman is Mithradates eldest surviving son by his first wife. Ate is a daughter from his second wife, so Shalman's half-sister. Played in character, ie not distorted by Macalix
, she likes Shalman a
lot, and despite lies to the contrary, Shalman gets on well too with Ate; they are brother and sister brought-up together in uncertain times for the royal family.
The succession should be:
Shalman
Shalman and Polonova's issue, if any
Ate, if allowed (male line only? Don't know, Bruce said he would check)
[Specifically not allowed, Ate and Macalix's issue, as Galatian]
Demetriaces
After I don't know.
Cambyses is Shalman's great-uncle by blood. Ate's only by marriage (ie, not related by bloodline).