Best Practice of SMB in OMV

Supposed there are 4 accounts in my OMV:

1. Acount: admin; Password: 12345678. This acount is only for GUI login.

2. Acount: root; Password: 123456789. This acount is root in Shell.

3. Acount: myself; Password: 123456789X. This acount is my real acount in Shell.

4. Acount: itself; Password: 123456789Z. This acount is the real acount of my sister in Shell.

Now, I log in to OMV GUI with admin, and I create a new shared folder in Storage/Shared folders: testDir. I set it myself read only, and itself read/write.

I go to Services/SMB/Settings, it looks like:

I go to Services/SMB/Shares, add testDir as a shared folder. It looks like:

Next, I found that both myself and itself can create a new file:

-rw-r--r-- 1 myself users 0 Mar 20 19:36 myself.txt
-rw-r--r-- 1 itself users 0 Mar 20 19:37 itself.txt

In my design, myself account should not be able to create or write any file in testDir, which is the private of itself account. This is problem one.

Next, my sister want to use SMB service in Windows 10. She found that she could not login with Acount: itself; Password: 123456789Z. This is problem two.

All we want is: create a private dir testDir for my sister. Only she and root could read/write the dir. Others could read it only.

How could we do that?