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 | JEAN GREY | PORTRAYED BY FAMKE JANNSEN
"All kind of things." - X1
"This is the only way" - X2
"Kill me before I kill someone else" - X3
"Where else would I be?" - X4