Hi, there was a known bug with samba system that it would report root capacity with the *nix systems. But I guess yours' is a little bit confusing. I strongly suspect that you have create all 3 sub-volume on the same volume (presumably you would be using Btrs)
Please check the following
Check Storage manager, check how many storage pools and volumes you have. If you want to use 3 drive as 3 separate volume, you should have 3 pool and 3 volume
Check Control Panel -> Shared Folder, you should have at least 1 shared folder on each volume, it could be chosen when created or be moved afterward.
Hope this solve your problem