Please use this tutorial on how to make collaborative documents on Google Docs. With Google Docs, multiple authors can make comments, edits, and suggestions all on one document.
Please see this article on features within Google Docs that may make your writing & research process easier.
KEEPING TRACK OF CONTRIBUTIONS:
In order to make sure that everyone contributes fairly to the project, students should keep a spreadsheet tracking team contributions. I have provided a sample spreadsheet for you to view below. With Google Sheets, you can open access to the spreadsheet to all group members, or additionally, assign this task to your Editor.