I know this is trying to teach the distinction between you singular and you plural, but it is really annoying to be forced to use you all or y'all, which are distinctly southern dialectical forms, and never used in writing except when trying to show a person speaking that dialect.
I agree. Unless these words have the meaning of everyone with no exceptions, it is a mistake to expect "you all" in normal English. Otherwise the normal plural in English simply uses "you", and it is left to those communicating to figure out the meaning. This habit may change in the future, but as it is used now, "you" is all that is required in English.