All packets have router IP when they arrive at kerio control

I have four sites on my network, each site has a microtik router that connect them together. I only have one internet connection at my central office. My internet is connected to Kerio Control firewall along with my central office router. I configured the Kerio to give internet only to specific users. But as all client traffics go through router, they all have router IP. If I login on a client, all clients use that account. Because from firewall sight of view, they all have same IP.