User Sync configuration

I have four WP sites. The sites are restricted - meaning they do require a user name and password to be entered before they can access. I would like to set up one site to be the master, and the three others to be sub-sites. Because I don't want users to change passwords in the sub-sites, I will look for a way to prevent password changes in the sub sites. what I really need though is to ensure that the user sync to the sub-site takes place as soon as a user changes their password. Is this a valid scenario? Thank you in advance for any support you can provide.