Y’all is colloquial and not formal. I thought the OP was looking for a formal way of doing it. It’s also regional. Nobody I know uses y’all for anything except when they’re putting on a southern drawl. I don’t think it is accurate to tell someone unfamiliar with the English language that y’all is a proper form with regular usage.
When I address a class of 60 people to instruct them how to do something, I say,
“First, you take your xyz and do abc. Then, the next thing you do is do blah blah.”
Sometimes, if I want to be specific about something, I might say,
“Make sure you all do abc”
In that circumstance, I’m using ‘all’ to reference each specific person within the group of ‘you’. But it’s probably not a proper way to phrase something, even though people commonly phrase it that way. It would be more accurate to say, “make sure each of you do abc” I say it that way because I don’t want any one person within the group of “you” to forget that one specific thing.