Well what is the common point between the story lines? How are they interacting and what parts of each story are needed in the other to actually make it make sense?
You possibly don't need all of the stories. Ideally if the stories are strong then they should be able to stand just fine on their own without the others holding them up, but the real trick in story telling in this manner is weaving them together in such a way that while each story is good on its own they are in turn reinforced and enhanced by the other stories.
Not a game, but look at A Song of Ice and Fire (Game of Thrones), and think about how the story would really be if you cut out 90% of all the other 'story lines' and only read from one "point of view". Jon's story of him being the illegitimate son of a noble and going north to freeze on the wall while hearing bits and pieces of what is going on in the south is still a very compelling story all on its own, even if we don't hear a single word from Rob's point of view. Basically every single main character's point of view sections can easily stand on their own for a far shorter overall story, and have the potential (with some work to fill in the odd gap) to still be an epic story that people would read and love. Told all together is making an insanely long and detailed story to tell, but the whole can remain great even if you were to remove entire POV sections of half the characters.
So where are your stories tying together, and why do you feel that you need them all? Start from there, and then you can examine things in better detail to figure out where you need to go next.
