I had a great post, but a 'Cat-fit ate it. So...
These things are extremely locale-specific. Where one 'catter says her source is certain "y'all" is either singular or plural, I can say without a doubt it's always plural in my location.
"All y'all" is an emphatic plural. Suppose I'm in a room with six people and I want to invite the two I'm in conversation with to dinner: "Y'all come over tonight to eat." Then if I want to include the rest (some body language included) I might say "and all y'all come over about eight and we'll watch the game."
"Y'all's" is pretty common where I live, but you'll never see it in print. Most folks here might say it in casual conversation but don't consider it "correct."
"Enforce" would be pronounced something like "en-FOE-werse," but in other parts of the South you'll hear "en-FOE-ahs." Like I said, there's no definitive Southern dialect. Here in the Upstate of South Carolina we have at least four distinct native variations: mountain, sandhill, piedmont and what you might call Upstate Black. All quite different, and that doesn't even include the transplants from Charleston, Georgia and Tennessee.
-HM