Maybe a combo of 1 and 4.  Where maybe one of the characters has been kidnapped and is being experimented on and the others have heard about things in their villages or such and maybe a seer even comes into the villages and helps to bring them together and tells then if they want to find out the truth they need to find the other one.  Which leads to the experiments and maybe the real reason behind the war? Then can go from there with more plot twists or such.  That is just one option.  Am open to others though.  All of the ideas have merits but I like the idea of combining some in some ways.