The third way is how it's done in StaffingResourceContactInfoViewModel. It uses Conductor<T>.Collection.AllActive. You'll still have to activate each VM once, but from that point on the conductor manages deactivation and potential reactivation automatically. You can then either bind to the Items collection and layout the 16 views in an ItemsControl, TabControl etc. or if you need to access them individually than you add properties on top of the Items collection that pulls out know VMs.
To reduce the constructor those 16 VMs can implement an interface by which they are exported and do an ImportMany. You can see that done in StaffingResourceDetailViewModel. It imports IEnumerable<IStaffingResourceDetailSection> and each one automatically becomes a tab. I can add new tabs without having to touch the DetailViewModel at all. Just add another VM that implements IStaffingResourceDetailSection.