Need to be careful that you're not being the well-meaning villain in all of this. Reinforcing a social stigma of talking about salary problems with other people

Need to be careful that you're not being the well-meaning villain in all of this. Reinforcing a social stigma of talking about salary problems with other people who may be having similar issues opens up a world where an awful lot of abuse can go unchecked, and even though you're quietly working behind the scenes to resolve it, it doesn't change that for several years those employees may have been making 40% below what they could have been earning. If they had found out about it, and then decided to look for another better paying job, they could potentially be significantly further along in achieving their financial life goals compared to where they are now. Underpaying people isn't an entirely victimless scenario, and it might be a little bit paternalistic for you to encourage keeping them in the dark while you gradually sort it out.