I have a student from Virginia who says she has heard the use of all y'allses; does anyone know about this? Is it that the second person plural being used is all y'alls (with the -s at the end here not indicating possessive but plural) and then the es is the possessive being added to that?
All y'allses is very Southern idiomatic speech, meaning, all of y'all's (you all's), or that all belonging to y'all.
all is a relatively common way of making an inclusive pronoun. Someone might say of a picnic table of food, "Did you make any of that all?" If the speaker is addressing several people, they might say, Did y'all make any of that-all?
All y'allses is not common except in in certain parts of the south, and definitely indicates possession, as opposed to plural. Plural of y'all is y'all, as it is a plural pronoun; sometimes all y'all may be used as the plural if it is a very large and diverse group.
But it more likely means, is that-all y'all's?
People in Tennessee (Knoxville/Memphis/Nashville) speak this way, and it is spoken in other Southern areas as well. It is very informal slang which is avoided by people who don't want to sound uneducated, or exploited by those who want to be identified with the deep south.