How does co-op progression saving work exactly? What if I'm a few story missions ahead of my friend(s) and they join my game? Will everything they do in that session be saved or will only my progress (the host) be saved? Will everything they do except mission progression be saved -- such as items, skills, etc? If everything except mission progression is saved, how does that work out? Will it be awkward/unfair playing with a friend who has progressed decently further?
The reason I ask this is because it seems to be a problem getting 3 of my friends together at the same time. One of them will leave shortly after another gets on or something along those lines. This week has just been hectic all around. Then, I'm stuck with my other friend who doesn't want to progress any further into the game when it's only the two of us, because she thinks if we go too far, it'll be off-balanced with the other 2 friends once we all get together. That then leaves me wondering the same thing, so I end up not playing solo...when I really want to, because I'm enjoying the game and just want to play it already. 2 days after release and I'm only at 7% completion with 3 quests done...saddening.