In my WIP the MC's father (who is an influential general) joins in a plot with the council to assassinate the current King. The kingdom has been at war with a nearby confederation of barbarians (sort of like the Gauls in Ancient Rome) for nearly a decade and have gained a foothold in the territory but at the cost of the lives of many soldiers (including the father's eldest son who was his best general) and townfolk who live on the border. The King hoping to focus on rebuilding from all the battle, wishes to withdraw from the barbarian territory and foster a ceasefire. The father however sees this move as a betrayal of everything he and the soldiers have fought and died for and he knows that it's only a matter of time before the barbarians just invade full force. He feels complete subjugation of the barbarian population is the only way to ensure a lasting peace for the kingdom. So he joins in the plot to assassinate the King. Is that a strong enough reason to kill a man he swore loyalty to and as a consequence put the king's family in danger as well? Or is it just an overreaction? I know historically speaking kings have been assassinated for less but I want to make the father at least somewhat sympathetic and not just another greedy, power-hungry despot, who just wants to be king for the sake of it.
Honestly it depends on the character and the motivation for serving the King in the first place. If he sees his service as being to the nation or the monarchy, and sees the incumbent king as threat to that system, then it wouldn't be a problem for him to join a militia that wants a coup in order to restore national greatness. Perhaps a good model to look at would be the Ulster loyalist paramilitaries in "The Troubles" in Northern Ireland. Basically you had people there that were so committed to their loyalty to the British Crown that they felt it necessary to violently defy said Crown when they didn't think it was adequately defending itself. So really there you had a three-way mess between the British government, Irish republican paramilitaries that wanted to break away from the UK, and extreme Loyalist paramilitaries that thought it appropriate to take the law into their own hands (and which were seen as terrorist groups by the government they sought to uphold). http://en.wikipedia.org/wiki/The_Troubles
Yes, the basis for the father's motivation in serving the king in the first place is most crucial. Does he have to be the one taking power after the assassination, or does he seem to realize that only after things can no longer be undone, and he should take control of the situation for the good of the country? (probably motivated by the same reason that led him to kill the king in the first place, though he could of course be corrupted by the power he took for originally more altruistic reasons). You might look at Cromwell as a similar case...
I think it could easily be a "valid" motivation in the eyes of the character. Some readers will feel that it's morally unjustified; this isn't bad, but it could be recognized/utilized by you if you have some characters show disagreement with the father. Machiavelli's The Prince lays out arguments for such actions if you want to read some political theory on the subject.
In general yes. If you want to strengthen the motivation make the disputed region the fathers homeland so he has the added motivation of his familys safety.
I'd be okay with it. Have you read Brian McLellan's Powder Mage trilogy? It opens with one of the MCs spearheading the bloody assassination of the king and the entire upper government. At first it makes him seem like a possible villain, but as we read on and see his motivations he becomes fairly sympathetic. Still a morally ambiguous figure, I'd say, but certainly not a villain.
Is the father loyal to the king or the cause? What buildup or sequence of events, internal or external, led to the split in loyalty? I personally really like to use internal dialogue to tell that part of the story. Few of us are truly impulsive decision makers. It takes a lot of thought and debate and internal struggle to make such a major decision even with a catalyst or two to spur us on. I would say this is especially true for people with strategic minds. Emotional decisions can be hard to come by for people like that.
