Hi David,
Thanks for reaching out.
The only way to ensure that folks can add and edit sites to an event is to do the following things:
• Go to Events → Settings → Community in your wp-admin and limit the ability to submit events to only those folks with wp-admin user accounts.
• Turn on User Registration within WordPress itself so folks can make accounts on your site. Here’s a good guide on how to do that → http://www.wpbeginner.com/beginners-guide/how-to-allow-user-registration-on-your-wordpress-site/
• This way, folks can edit the events they submit.
There is not another method for this that our plugins provide, nor are we able to help with customizing these features or adding extra features. Learn more about this here: https://theeventscalendar.com/knowledgebase/what-support-is-provided-for-license-holders/
Once you do the following things, then for anyone to submit an event they will have to be logged in and would have to use the password to get past that page.
If you just want a password-protected page, but do not want people to have to have user accounts, this is unfortunately not possible at this time.
Please let me know if this helps and if there are any other issues or questions I can try to help with!
— George