I don't think that your issue is related to the ".TemporaryItems" folder, as the problem only seems to happen when trying to open a file created by other user.
Check the group permissions on that share, of course the users have to belong to the same group and that group needs write permission on the "Share", and you need to enforce that new files are created with that write premission for the group.
Found out this is due to the QuickLook Office plugin in the system.
Disabling this plugin will fix this behaviour, unfortunately you can't use QuickLook anymore for Office documents.
1. Open Terminal
2. Enter or copy this command and it will be fixed :
sudo mv /System/Library/QuickLook/Office.qlgenerator /System/Library/QuickLook/Office.qlgenerator.bak ; killall Finder
Try setting the permissions of the folder that contains all of the "read only" and change to "read and write" for all users ( or certain user if you olny want certain people to acces them ) and apply to "enclosed items". In my case the files were on the server the office is sharing so I change the permissions on the server so that everyone can acess the files.
here is a link in case your not familiar with the process.
This solve the problem for me.
Turning preview off (right click folder->show view options->uncheck show preview column) fixed the issue for me. I played with this a bit more and in my case, the preview is definitely what was causing the server to only allow read only. That was only happening for larger documents that took a while for the preview to load; while the preview was loading I tried to open repeatedly and kept getting "read-only", but once the preview loaded the document opened right up. Which led me to another solution for those (like me) who want to keep preview on--switch to the file list view in Finder, which doesn't have the preview pane, and documents open right up with no read-only issue.