You sure can with one exception I would suggest. Create two libraries (Fred TV, Brenda TV) If I could suggest you create each library with a minimum of two storage locations, for example have a C:\TV and C:\Fred TV for the Fred TV library.
This will allow you to store shows you each watch in C:\TV and shows only Fred watches in the C:\Fred TV. When setting up a recording you can specify the library and storage location for the recording.
So for shows only Fred watches you would specify to store the recording in C:\Fred TV. When setting up a recording you both watch specify C:\TV for the location. You then configure Fred’s account to have the library Fred TV.
You’re welcome. One other thought I did have with this setup is that if you login with the Admin account instead of the Fred or Brenda accounts you will see shows listed twice in the Recently Added if they are shows you both watch. This is because the C:\TV folder is in two libraries.