In my WIP, the half-brother of the MC and the MC's maternal uncle plot to take the kingdom away from the MC's family. The half-brother is the result of the MC's father and the father's first wife (who was his childhood friend he fell in love with.) They had a life together until the father's royal calling forced him to take another bride to solidify an alliance (In the world I'm writing polygamy is common practice). The new woman by default of her royal heritage became the primary wife (I.E. the one with all the political power). They had a son together (MC's older brother) who automatically became the heir, passing over the son the King had with his childhood romance. Obviously the first woman is pissed at losing her position so she tries to kill the boy. It fails and she and her son are banished. When the story starts, the half-brother has grown older and is convinced he should be King. The MC is sent to nip the problem in the bud before civil war breaks out. But since the MC is the youngest son, I'm not sure how much of the back-story he should have previous knowledge to. Should he know that he's being ordered to kill his own half-brother? Would that add much? What reasons would his father and his mother have for not telling him about what had transpired before hand? Any thoughts? Thanks in advance.
This is entirely dependent on how you want it to go. The MC will know primarily what he's been told by his parents and their advisers. How complete or true that information is depends on how you want to portray the situation and who the good guys are. If your plot has the MC's family as the good guys and their opponents as bad guys - then I'd assume that most of what the MC knows is true. If the MC's family are actually the bad guys and the half-brother is sympathetic - then this is a voyage of discovery and I would assume that most of what your MC "knows" at the beginning is false. And of course if you are in between those options - you can have shades of gray between those two poles.
I think your MC should accept his mission without prejudice, with interests concerning the prosperity and prolonged peace of his kingdom. The actual back story, if introduced in the fashion of an earth-shattering realization to the MC, could make for a pretty sick plot twist. Of course things will get complicated if the MC finds out that his mark is actually his blood brother. I am sure you have your own story details down pat, but that twist opens the door to so many possibilities. Perhaps they ally against a greater threat within the very kingdom they fight for. Either way, i really like what you have going on here.
The rule of thumb I would use is: if the MC benefits from foreknowledge (i.e. his life is made easier) he shouldn't have it. If foreknowledge will lead him into difficulty, he should have it.
