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 | PSYLOCKE | PORTRAYED BY OLIVIA MUNN
"Going somewhere?" - X3
PSYLOCKE WILL RETURN IN X-MEN RI5E