I don't think "you all" is necessarily bad grammar. But I don't think "these ones" is either. I think it's just more specific.
Y'all is not wrong in the right context.
I would not use y'all in formal writing.
I hear "I seen" a lot now. A coworker of mine is from Ohio. I don't like it, but whatever.
"In the depth of winter, I finally learned that within me there lay an invincible summer."
4a, mbl, low porosity, normal thickness, fine hair.