BuddyPress.org

This plugin will force usernames only across the site. If your usernames are their real names, that might be a fix: https://github.com/r-a-y/buddypress-usernames-only

Small caveat from the plugin readme:

By default, display names are enabled in the member header on profile pages. If you prefer usernames to be shown, add the following snippet to your wp-config.php file:

`define( ‘BP_SHOW_DISPLAYNAME_ON_PROFILE’, false );