Re: different domains ( sites ) using same users
it’s not impossible, but may be problematic depending on your hosting. Some hosting companies allow remote connections to the database, others do not, and most are whitelisted depending on the originating ip address. However, if all of your domains are in the same place, it shouldn’t be a *huge* problem.
Just look around for what to replace the ‘localhost’ with in your config.php file (completely arbitrary example: mysql344.dbhost.com) or something like that.