People where I am from call everyone "you guys" - men, women, trans, doesn't matter, everyone is just "you guys" even when it's a woman addressing a group of women.
The literal meaning isn't gender neutral, but in actual practice, it 100% is.
As for "y'all" or "you all", I don't see how it could possibly be interpreted as offensive to any gender.
I don't see the issue with using the term "guys" in the plural when referring to a group regardless of sex. That would align with the definition of the word. I'm pretty sure that's how they meant it.