It would benefit from a period, and I can’t tell if they’re trying to be sarcastic, but the use of y’all is fine. Y’all is an American-English word most similar to the Spanish vosotros. Y’all’s-selves is a more specific dialect mostly found in the US south east, but it is a word too. Y’all fills a hole in the language and I don’t get why people hate it so much. Y’all’s-selves really only serves the purpose of adding an emphasis on the collective nature of yourselves.
Just FYI, y’all is pretty much confined to the US South. You almost never hear it in other regions.
That’s also why there’s so much hate: because “y’all” is so strongly associated with the South, and the South has a bit of a reputation in the rest of the country. Some of which is deserved and a lot of which isn’t, but it is what it is.
