Connecting 2 or more Wi-Fi devices to the Internet

Hey

I got an ISP that has assigned me a static IP address that is obtained via DHCP. For the connection to work properly, a MAC address of the computer connected to the Internet must be entered into the ISP's system.

I wanted to make a wireless network, so I asked my ISP for permission. They said I could only use my router as an access point and that I had to turn off the DHCP server. I am not allowed to plug in the RJ45 into the WAN port.

Now, in the 'access point' mode, can I somehow connect 2 devices to the Internet using the Wi-Fi? It seems that only the device that has its MAC address entered into the ISP's system can connect to the Internet.

If the above is not an option, what if I used the WAN port and entered the router's MAC address into the ISP's system? Is there a way for them to tell I'm breaking the rules?

In short, how do I connect multiple devices to the Internet and don't get busted?

Thanks for your help in advance and sorry for the newbie question.