Restricted document access in shared group

Hi,

I created the following file structure (all Excel files) in a Teams group:

- *Master file*

- File "Susi"

- File "Jake"

- File "Lisa"

- etc...

What I would like to achieve:

1) Each member of the group can only open the respective file (e.g.: Susi can only open the "Susi" file but not "Jake" or "Lisa")

2) None of the members must be able to open the Master file

At the same time, I linked all Sub files (Susi, Jake, Lisa, etc.) into the Master file. So, whatever is inserted in a Sub file will appear in the Master. 

I already tried to put passwords on the respective files. However, that did not prove to be useful, since the users who have access to the master file had to apply all sub file passwords each time when refreshed.

My idea is that the master file updates whenever something changes in the Susi/Jake/Lisa-files, yet the respective people can only see/access their file, while other parties have access to both, the master file and all the sub-files.

I am grateful for any help I can get and thank you guys in advance.

Best

JJ