To do this with a plugin outside of your Factions plugin, use PlayerCommandPreprocessEvent, check if the command is /f home & check if a player is in another faction's claimed land. Cancel if so. To do it in your Factions plugin, just add a check to the Home subcommand
Is it possible to add some code to FactionCommand.php to prevent people from using it instead of doing it the way u ask?
Check option 2... Depends on your Factions plugin's API (or how they save claimed land and factions if they don't have an API...).