No where is used “username”. Everywhere is use “display_name” which is make in the wordpress core to use publicly.
You can change display_name of your desire users in back-end user profile edit page (Change Display name publicly as).

There are many places to show name in this plugin and everywhere there is filter to change also. But you need code to change where you want. eg. If you want to change in directory use fep_directory_table_column_content_name hook.
My suggestion, you can create your company profile separately to use so that you can name it how you like without coding.