Is there a module which allows users to edit text together?
Maybe you want to consider using the Paragraphs module for this. Here are some quotes about it (from its project page):


  Paragraphs is the new way of content creation!
  It allows you — Site Builders — to make things cleaner so that you can give more editing power to your end-users.
  
  Instead of putting all their content in one WYSIWYG body field including images and videos, end-users can now choose on-the-fly between pre-defined Paragraph Types independent from one another. Paragraph Types can be anything you want from a simple text block or image to a complex and configurable slideshow.
  
  Paragraphs module comes with a new "paragraphs" field type that works like Entity Reference's. Simply add a new paragraphs field on any Content Type you want and choose which Paragraph Types should be available to end-users. They can then add as many Paragraph items as you allowed them to and reorder them at will.


Some other questions on Drupal.SE where the Paragraphs module has also been suggested as a possible answer (which may help for more inspiration about what kind of things you can do with this podule):


Modular Drupal content-type (variable sections).
Simulating TYPO3-Template-Engine.
Alternative to Field Collection.
What is the best method to allow a user to attach dynamic, custom content sections to a node?