Sngine has only 3 user groups
1- For admins
2- For moderators
3- For Users (default group) so when a new user register his user_group set to 3 be default

And to add a new user group you will change some files (both view => HTML and code => PHP).
For example:
1- admin panel -> edit user
content\themes\default\templates\admin.user.tpl

includes\ajax\admin\user.php

Edit this will enable you to add new user_group “4” for example and change the user_group for any user from admin panel
For Pages, Groups and Events:
You can find all function related to the pages in
includes/class-user.php

The same thing for groups & events check the file to learn more …
Now you want to enable only the admins, moderator and users with user_group 4 to create/edit page So you need to change the check condition at top of create_page() function and edit_page() function and so on …

To be like that

Which mean if pages disable by the system and at the same time user group is 3 so this user can’t create a page
However admin, mods and user_group 4 people can continue …
And the same thing you will do for groups and events and so on.
That’s it Happy Sngine