Redmine

I have a lot of feature tickets (issues) that I'm currently trying to organize, i.e. to assign them to different project versions. Now I'd like to know how to deal with tickets that have parents. What are your thoughts?

Example: User management

  Parent issue:   Introduce frontend users
  Child issues:     - Let a backend user create a frontend user
                    - Let a backend user delete a frontend user
                    - Let a backend user modify the data of a frontend user
                    - Let a frontend user authenticate
                    - Let frontend users change their password               (implemented later)
                    - Let frontend users change their theme                  (implemented later)

This makes sense as I think. But if I want to realize it in 2 milestone, how should I deal with the parent task? Consider that in MS-1 the parent task would not be completed until MS-2 gets finished. Think of the roadmap. How could I organize this best?

Thoughts:

Should the parent issue gets assigned to a version?
Should the last two issues (MS-2) get another, new parent?
Should I generally avoid having child issues in different project versions?
Should I avoid parent issues?
Should Redmine prevent having child issues in different versions?
Should I consider using (temporary) sub-projects for the milestones (each with its own project version)? Would you recommend that in any case?

Have you ever done things in this way? Or what could you suggest?