I'll add into the speculation... just for fun. Though I'll go back further than most will go in regards to the story. All the way before the beginning of the events that have transpired since the king's death.
The Crone is the start of it all. Far too often she has shown a connection to the Royal Court and a desire for power, especially magical. Whatever her appearance she's obviously capable of hiding or changing it at will via magic. She has also shown a willingness to kill, as with indicated by the old Truthsayer, your mentor. At this point it shouldn't be too far of a stretch to solve that murder. To borrow an old saying “Poison is a woman's weapon.” That is to say, it doesn't require brute force or as much effort as a direct confrontation. Nor is it as easy to trace back in many instances. Primrose was easily framed for the death of Marek and would have been sentenced if not for the intervention of the MC. As for her motivations, the old Truthsayer would be far less likely to not have moral issues over the MC's use of this powerful magic. The Crone could give a shit less about whom you do or don't corrupt and pervert on your rise to power. Their pawns and acceptable casualties on the way to something else.
The Crone enlisted either the Princess or her sister Lilith in the ways of magic in effort to further her own power. Just as her statements of what she could have accomplished if she had the spellbook the MC gives her previously. And she fucked up beyond her wildest dreams. Three pieces of information are important at this point; the legend of Samarra's people, the Fae Genocide Vision, and the old Truthsayer's vision of human extinction. Either the Princess was lured to the roof and Lilith was killed while the demon transferred itself to the Princess, or the demon sought to break the Princess' will by killing Lilith. The original Selena is trapped inside her own mind. I suspect that it was the possessed Selena that killed her father in order to position itself into a place of power in preparation for conquest.
With the knowledge, prior to the king's death, The Crone fled and sought a means to weaken the defenses of the possessed Princess in hopes of removing the demon. Failure is the wholesale slaughter of every living creature in their world, human and Fae alike.
As for the Fae King, he targets the MC specifically because it was the MC in the vision, not a random truthsayer. And let us be honest, the two-pump chump is just looking for glory because he can't please his woman.
The real question is... who the fuck the MC really is in all this. When The Crone attempted to cheat and increase his ability to learn she found someone had already done that. The side effects of the spell being the player was lazy (as he technically already had the knowledge) and the constant scorn from others such as his uncle. Even The Crone asks this question as she realizes she is playing someone else's game. While an excellent in game explanation for a New Game+ feature, it still has in-game ramifications. Thus someone we don't know about, and have yet to have any building toward, is also active inside the realm of this little game. Either someone who managed to go back in time and find the MC to perform the alterations... or someone else that knew what was transpiring and attempted to create a way out.
Granted, the Fae war may allow for an escape of the wholesale slaughter... but in honesty it would simply serve a possessed Princess' goals; to hasten the willingness of the human population to accept possession. The entire key to victory isn't in genocide, but in killing the Princess as quickly as possible. But the risk is galvanizing the entire human population into war. The MC is, honestly, the only way to escape a zero-sum game of war.
On a side note, it sucks DAZ has had issues on my comp and I'm not very good with coding. Otherwise I'd probably have started up a game, myself. Anyone recruiting a writer/designer?
