It's important to keep in mind (maybe you misunderstood what was mentioned in the game) that the king first consulted oracles on his own initiative, some of whom persuaded him to believe in a prophecy that his son would be responsible for his downfall or death. It appears that the queen mother attempted to bribe or recruit oracles to mitigate the impact of others on the king, thus protecting her son by influencing the king's ever-changing opinions. It is said in some conversations with Cass, and possibly with the mother, that these oracles, were dishonest charlatans, they exploited their tremendous influence over the monarch to gain personal power. Apparently, several of them served on the council.
It seems that it was an informal alliance between Cass, a few advisors in the council and the Queen Mother that finally got rid of these highly influential false prophets, although it was mainly Cass who accomplished this thankless task. Some of the advisors at the first meeting with the prince mentioned that the situation had become chaotic with the numerous oracles present at court and at the council, bordering on disorder and certainly internal warfare for power at court, especially with an irascible, fickle and mentally unstable king.
We can only assume with some uncertainty that the king was apparently responsible for the death of his first wife, but he didn't seem to appreciate it, and no doubt his eldest daughter as a result. Yet Cass may have been led to believe by her hatred of her father that he was responsible, and by her own family on her mother's side. I have no idea what happened to Conrad's father, the king's relative. Once again, the king could be responsible for the disappearance of other individuals in the court or in the nobility of the kingdom, but we must also remember the period of unrest and wars that took place during the time of the Red Emperor and undoubtedly after his death.
In my opinion, you see Cassandra as a victim of circumstance, which is technically true, but only in part. However, we mustn't overlook the hatred she feels towards her father, the hostility she shares with her stepmother, and the jealousy towards her half-brother, the heir apparent due to his male gender.
The incident between Elis and Cass reveals a complex dynamic of love and hate, aggression and competition, and a clear rivalry for the throne. It's no doubt for this last reason that the Queen Mother can't stand Cass; apart from her character, she's even a threat by definition, and court intrigues abound. Lady Alaina has seized the opportunity of this accidental quarrel between the two of them to convince the King and Queen to keep the young prince away from court (to keep him away out of fear for the former, and for the Mother to protect him from intrigues and threats).
It seems obvious that she aspires to rule, motivated by revenge as much as ambition, with the support, voluntary or forced, of her half-brother, whom she deems essential to the fulfillment of her designs. In her cynical, pragmatic view of life, she believes only that the ends justify the means, and that the most ruthless prevail.
Also, the sacrificial ending with Cass that you mention only works if you as MC decide to do it, otherwise her plan proceeds pretty much normally (which is inconherent, that Elis does nothing to prevent it, so it's a pretty forced choice and intended as dramatic), with the prince ending up quite often in prison depending on the branching chosen.
So yes, she's a victim of circumstance, born a woman and therefore excluded on principle from the succession; her mother died in troubled circumstances; she's hated and despised by a good part of her family (the father, the mother-in-law, and many at court fear her or distrust her and her intrigues).
She is undoubtedly manipulated at least in part by her mother's side of the family in her resentment of her father and desire for revenge, yet she is unscrupulous and ruthless, and will stop at nothing to satisfy her personal ambitions. Cass believes that a true ruler must be prepared to do whatever it takes to consolidate his power, even if it means betraying allies and killing those closest to him, which is why she asks Elis to “ suicide ” her in a branch of the game, but also for love.
For me, Cass is clearly responsible for her actions from beginning to end, despite the initial circumstances of her life. At various points she could have made different choices and taken completely opposite routes, but she's a stubborn person who will never listen to reason. So for me, she's someone who can't know any form of redemption in her arc, which is what the game wants by design.
The mother has dirtied her hands far less in comparison, and has doubtless resorted less to dubious methods, even if we still don't know what she's up to with Lady Alaina and the elves of her native clan. It's likely that these two women will try to influence Elis to become a more compassionate and just sovereign with regard to the fate of the kingdom's elves, or perhaps Lady Alaina will try to push the future king to promote them through partisan politics in favor of the elves.
