I think you need to undo what you have done on the 10.9.3 Mac. If you haven't got any new data on that Mac I would erase the disk & start again. If you have important files on that 10.9 Mac you will need to get them off somehow (probably reversing target disk mode).
Disk Utility will be able to erase the HD if you boot into recovery mode. Use the erase option to delete the internal disk.
Install 10.9 again.
When you run the setup assistant, avoid using your old username on the 10.8 Mac - create an admin user, then use that admin user to import the old users as described below.
The next step is to just use Migration Assistant to move the data from the 10.8 Mac.
It is /Applications/Utilities/Migration Assistant, open that connect your Target Disk Mode Mac.
Then you can tell it to import …
- Applications (old apps may conflict - uncheck if you have old apps on 10.8 possible)
- User data (your files - should migrate OK)
- Other files (anything you put outside the home folders, and may include pieces of old software).
I would play it safe & only select the 'user files', so long as you can stand installing your applications manually.
That will give you the contents of the home folders with the correct permissions.
If you really need the same data on each Mac you should only sync selective folders - copying the entire home folder will cause issues with the different OS versions for application preferences etc. I also think you should probably avoid syncing the file permissions if possible (just sync file contents) - each Mac may have a different 'user id' depending on the order of the account creation.