You only really need multiples of Media sets and jobs - although to make life easier two backup to disk folders would help
You don't say if you want to append to the files so I'll assume you don't (for simplicity)
Monday to Thursday
Create a Media set with overwrite protection 6 days, Append 0 days
Create a Backup job that is scheduled for Mon-Thurs (whatever start time you like) and uses the B2D location and the Media set.
Note 6 days will mean Monday's media is available to be overwritten the next week, same for Tuesday etc.
Friday
Create a Media Set with Overwrite Protection 27 days, Append 0 days
Optional: Create another B2D folder
Create a Backup Job that is scheduled for Fridays and uses the same B2D location or the optional one and uses the friday media set.
Note: 27 days allows the backup media to be available for overwrite 4 weeks later