The plural of Y'all is "all y'all"

"Y'all is typically used only in informal situations, and is frowned upon in (and even excluded from) formal speech and writing. It is sometimes used as a dual pronoun to refer to only two people, with a related form "all y'all" used for plural contexts. The possessive form of y'all is y'all's (e.g. "I really like y'all's house."), and the possessive form of all y'all is all y'all's. While y'all has begun to spread to general US English, all y'all and y'all's have not; y'all and your are used, respectively. In most areas of the South however, "all y'all" is never heard but simply "y'all" for two, ten, or ten thousand people."

- Wikipedia (http://en.wikipedia.org/wiki/Y%27all)

I am *so* amused.