The suggestion is to install FileMaker Pro on that server and open the file.
Then your users use Open Remote to find the server and select the hosted file that they want to open.
This is how FileMaker is designed to work. It does not support filesharing and your current set up can result in a damaged database file--not good.
The copy of FileMaker installed on the server must have sharing enabled. In FileMaker 13, you click on the Share icon and choose "share with clients". You then click the needed control to turn sharing on. If you do this while you have the file you want to share open, you can then enable the file for hosting from the server. Click the file's name in the list of open database files to highlight it and then select the "all users" option.
Now your clients should be able to find and open the hosted database file from their copy of FileMaker Pro.