What problems are your current settings in Manage | Security causing for you? Can you open it with a full access password?
Sharing is set up by selecting options from the File | Sharing. Once these options are selected, you can open the file on the computer where the file is stored and up to 9 other users can use Open Remote to find and open the shared file. Do not attempt to put the file on a shared directory and have each user access the file by opening it directly as this can damage your database file.
Open the databse file and then open Sharing | FileMaker Network...
Click "On" to turn network sharing on for your copy of the FileMaker application.
Select your file in the list of open files shown in this dialog and select the "all users" option.
Now, other users on the same local area network launch their copies of FileMaker pro and use Open Remote to access the same file. Each user can use the same account name and password or you can use Manage | Security to issue them individual accounts and passwords.