seems to me that the second answer would be correct if you were trying to contract the entire phrase "you all will" and didn't want to say "y'all'll"
"If y'all can line up right over there against the wall, ya'll be issued a bullet to the brain for trying to push your fancy book-learning upon our children."
no subject
"If y'all can line up right over there against the wall, ya'll be issued a bullet to the brain for trying to push your fancy book-learning upon our children."