Re: Billing order.
I think its safe to say that the 14 actors who attended the Comic-Con are the principal/main cast.
So they are the ones who would will get a billing in the posters.
X-MEN RI5E' MUTANT OF THE MONTH | CYCLOPS | PORTRAYED BY JAMES MARSDEN
"Stay away from my girl" - X1
"You don't say that, we gotta go back" - X2
"Not everybody heals as fast as you" - X3
"Easy pal" - X4