It is possible for users outside your network to access a hosted database via open remote, but you have to configure your internet router to permit it. Research "Port Forwarding" to learn how to set this up on your router.
Your local computers have Local IP Addresses like "192.168.1.101"
Your router would have a Local IP Address of "192.168.1.1"
Your Web IP Address (assigned by your ISP) can be viewed here http://whatismyipaddress.com
Your router needs to know what computer to send FMP requests to http://portforward.com
Google "portforward site:forums.filemaker.com"
Managed to get it working thanks for your help.