I believe SE has confirmed XII to be the first in the timeline. They haven't officially released a timeline but the one I've given is commonly seen as the most accurate one.

Why is Luso's case different from Marche? Because the developers said so. Marche and co ended up in a dreamworld. Luso is taken to the real Ivalice (to get there it either means his homeworld is not Ivalice in present day and that he simply goes to another world (Ivalice) or his world is Ivalice in 'present' day and he does indeed travel back in time to FF XII's era). I've read this in an interview on IGN I believe, but I'm fully sure that this is a fact. I'll try to find a quote.

I guess we won't know exactly how it is with FFTA2's world and the Ivalice Luso goes to until the game is released in english. =/