|The best way to do sharing in a "workgroup" network (as compared to a domain) is always to create user accounts on the computers with shares.|
Here's an example based on 3 computers, all with one shared folder on each.
Shared folder = C:\BrentShare
Shared folder = C:\CarolShare
Shared folder = C:\DavidShare
Now, on each computer, you want to allow the other two access to the share.
So, on PC 1 you would create two user accounts using the exact same username and password Carol and David use to logon at bootup (as described above).
You would then add those two user accounts to the ACL on the share C:\BrentShare and you would grant appropriate permissions (read/write etc).
Then on PC 2, you would do the same with user accounts Brent and David and finally on PC 3 with user accounts Brent and Carol.
Once finished, Brent could map a drive to the shares on PC 2 and 3 and never be asked for credentials and have whatever access you, as the admin, have granted his user account on those shares.
Now, this is a little bulky, which is one of the reasons we have domains. For your situation, I would simplify things by bringing in an extra computer and making it into a file server. Move the shared folders off of the other 8 PC's and onto the file server, do the sharing/user accounts on it. As per my example above, you would have a PC 4 as your file server, you would create 3 shared folders on it, add the 3 user accounts (once only) and then add them to the appropriate shares. and reduce your administrative overhead.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.