Does Y'all's really have two apostrophe's?

The house that you all own is nice.
The house that Mike owns is nice.
The house that y'all own is nice.
The house that he owns is nice.
Y'all's house is nice.
His house is nice.

I think officially, it's grammatically a nightmare. And by officially I mean prescriptively.

Descriptively however? Yeah, I think that's pretty common.

Personally, I'm not a big fan of the double apostrophe there. I'm all for wouldn't've though.

Actually, I don't think that y'all's should exist at all. As a possessive, it would be "you all's." Just doesn't sound right, does it? The plural of you is you, and the possessive form of that is your... I would just stick with that.
As a contraction, it would be "you all is." Disagreement of quantity! Y'all're seems acceptable... but it's still redneck talk >=o

"y'all" sounds so much more elegant than "you guys".

I like to say y'all and y'all's. It's really cute how people act uppity about grammar when not one single person in the entire history of Earth has ever bheen grammatically correct, though. :p

From what I can tell, and from what I understand from your (y'all's?) responses, it's perfectly understandable as a possessive word, and I like it and use it.

Also, I forgot about couldn't've, and other ideas for "not have" double contractions.

Anyway, it obviously isn't an original concept, but I think it's definitely grammatically correct, as far as I care to take grammar in my writing.

Thank you all and goodnight.

Seriously, Flying Mullet, what is your problem?