I would have setup this router as a WAP by using the LAN port instead of the WAN port.
And be sure you know, I do not offer any support for your current setup. The owner must be able to fix this as it's a little odd to have this many LANs plus the router and PC entries are going to be advanced.
Following is the topology of my network...
My router gets a IP 220.127.116.11 (DHCP) from my ISP by connecting via PPPoE.
Router Gateway is 18.104.22.168
My PC's LAN ip is set via DHCP to 192.168.1.100 and gateway as 192.168.1.1
In this case how do I access my Friend's PC and how can he access mine for file sharing.
Prior to buying a router we were connected directly via switch. Now router poses a problem.