I have tried to create a solution with SharpSVN to control the version of the file but I have not been successful so far, this issue is not an error that is occurring but rather a question as a way to find a solution. What do I need to know is how multiple users can work in the same Keyhole Markup Language (KML) file at the same time? Thanks.
KML is an XML file so for multiple users to edit and access the latest KML file, there are several possible solutions to consider.
Add the KML file to a shared repository (svn, git, etc.) to allow people to check in changes and update with changes made by others. You could post your KML file to a project on github.com.
Place the KML onto a shared network drive such as Google Drive and give read/write access to users as needed. Users can read or write the KML as needed and the changes will be accessible to other users.
Upload KML to a shared Google Fusion Table then allow users to edit/add the data. The data is then available to download as KML NetworkLink that auto-updates to the latest contents. Here are some tutorials using Google Fusion Tables.