It's possible, but it's a bit complicated doing that. You'd have to use CB Auto Actions to push data across your multiple sites to keep the user tables in sync. You'd have to synchronize their Joomla users table and more (basically any table that involves the user replicating data 3 times over). It's likely easier to just point all 3 domains to the same Joomla install then use an extension to display a different Joomla template, menus, modules, etc.. based off the domain name. You can find multi-site extensions below on the JED.
extensions.joomla.org/tags/multiple-sites/
Tutorial below could also be of help.
docs.joomla.org/Multiple_Domains_and_Web_Sites_in_a_single_Joomla!_installation
We don't provide any multi-site functionality so CB Auto Actions would be the only thing that could help here if you choose to keep all 3 domains databases separate, but that will be a significant amount of work and if you're not experienced with SQL I don't recommend doing it.