Permissions woes: can't copy files from Mac to Mac via network...

Copying files from Mac to PC has always been a huge pain in the ass for me, but I thought at least Mac to Mac would be easier - no such luck.

So I have a Macbook Pro and an iMac, both on Sierra, and although I can access/browse files/folders on my Macbook Pro from my iMac, when I try to copy files not only does it ask me for my username/password yet again (same login details on both machines) but when I enter the correct password it still prohibits me with the following error message:

Items can’t be copied to “...” because you don’t have permission to read them.

So I've repaired permissions on the Macbook, I've even tried to set Read/Write access to my entire hard drive for the user 'peanutismint' which is the same username/password on both my machines, but it still doesn't want to let the 'peanutismint' on my iMac have the access that the 'peanutismint' on my Macbook has.... I've also tried 'apply permissions to all subfolders' or whatever the thing is called but that fails with an error message too....

Is there something I'm doing wrong here? And there's me thinking Macs 'just work'....!!