For files, the `parent_shared_folder_id` is the "ID of shared folder that holds this file." For folders, the `parent_shared_folder_id` is the "ID of the parent shared folder. This field is present only if the folder is contained within another shared folder." That is, `parent_shared_folder_id` is only set for items inside shared folders and it tells you the ID of that shared folder above it.
The `shared_folder_id` is the "ID of the shared folder" itself. That is, `shared_folder_id` is only available for shared folders themselves.
In your example, the shared folder, mounted as F for user A and mounted as G for user B, would report the same `shared_folder_id` for both users. It would report `parent_shared_folder_id` if it is nested under another shared folder (e.g., a team folder).
