While using the Router as an Access Point you have to assign one of your ISP IPs to the Wireless computer.
If you want to use more than three computers, and the three ISP IPs. You have to create a second network. Use the Router as a Router, assign to it one of the ISP IPs, and assign IPs beyond the Router with DHCP.
However doing so splits your system into two Networks.
1. Computers on the Hub.
2. Computers behind the Router.