You know, as Iām thinking about this now, for @beck ās team, Pagico might be a good fit. It is cross platform, and includes what I consider to be the missing killer feature of a lot of apps like omnifocus - a timeline view.
Pagico can handle collaboration, project and task management, while assets such as links, spreadsheets and documents can be created using tools that share ubiquitous file types, such as xlsx, docx, etc.
A lot of the suggestions here have focused on how to do the actual collaboration of writing. Is that your main issue or will it be an issue of monitoring tasks among the members?
In other words - would a project management tool/task management tool such as Asana or monday.com be helpful?