Multisite User Sync will automatically synchronize users to all sites in multisite. Roles of users will be same on every site. If Role change in one site it will also synchronize to all site. If new user/site created it will also add to all site/users.

In one of my website it was needed to separate them fully for every product. So i use multisite. But it also needed to use same users (including role) for every site. So i write one plugin. I have searched for this type of plugins and i found none. So i upload it to wordpress plugin directory if somebody need it. This plugin works out of the box, No settings required.