here is my opinion of the story if anyone cares that is...
R* said something about being able to play as the protagonists and the antagonist so here what i think
michael get sent to kill someone in blaine county by the FIB who just happens to be close to Trevor making trevor look for revenge and someone tells him it was a member of the grove street gang so he kills a close friend of Franklins and by this franklin takes action by hunting down people in Rockford hills...
Overall this concept of being the antagonist towards the other characters may go against them but all 3 characters dont know something the player does
however this may be all wrong in the end and most likely be something completely different