Dead space 2 story confusing."Obvious Spoilers"?

Ok so I'm really confused on 2 things,,, I thought the story was bad enough already with all the confusion in it.. But does the necromorph outbreak happen in the Titan mines when tiedmanns guys remade the marker, the necromorphs from the sludge on the ishimura "now in the Titan mines" came to life and THEn the u unitologisists released it on the Sprawl in order to get Isaac out of his cro tube stasis... Also I'm guessing Isaac woke up a few hours after the outbreak AND finally why did the marker want to kill Isaac at the end lol WTF?? Did they purposely make this story so convoluted just so we have a headache I'm still confused -.- if anyone can explain pls