The client connecting to the above router is getting same MAC address of the router with different IPs. for example, my laptop is showing router's mac, same problem for all devices connected to the router. How to fix it?.
An AP-STA link assumes that everything on the STA end is one MAC address, as would be the case usually when the STA is a single machine like a laptop. The standard doesn't provide for sending a "final destination" MAC which would be necessary to have a true layer 2 bridge.
If your AP supports OpenWrt you can use other linking standards as mentioned above. If it's a typical ISP provided box with closed firmware you are stuck with either relayd, or moving your whole network to the LAN side of your OpenWrt router and using the ISP box only as a source of Internet.