Users, groups, permissions

Hi everyone,
Had a major breakdown and then upgrade of my home NAS and since now I have more storage, I decided to give the *arrs another go.
ATM, I am using a RPi4 with one HDD plugged into it (being used only for downloads, I think its NTFS). The OS is on an SD card (which is plugged into a USB card reader as somehow it fails to boot when inserted in the built in SD slot- will sort it out some other time). All media that I access from other systems is on NAS which is running samba with two shares (Movies, TV_Shows) and dietpi has both of these mounted.
The problem is radarr cannot move the downloads done by deluge (which does it on USB attached HDD), as my permissions are all over the place. I want to sort out the users (sonarr, raddar, deluge, nzbget, jellyfin, etc.) and put them into one group and then set all permissions to the download HDD accordingly, so that all media related apps can access the download folder and move the files around as needed/ planned.
I am attaching list of users, groups, and fstab.
Can someone please help?
Many thanks,
fstab.txt (1.9 KB)
groups.txt (1.0 KB)
users.txt (1.9 KB)

usually we use group dietpi to allow access between different apps.

Thanks, I have now dietpi as a group and user, all media apps are members of dietpi group and /mnt/HDD (where I download files) is owned by dietpi. I will update how it goes. Thanks again.

ps: On a side note, I would have preferred a unique user (e.g. mediamanager, etc.) to deal with all media apps and their downloads. Dietpi is the default user, I am guessing. Anyway lets see how it goes.