Usually you'll all be on the same "network" when you all log onto the router. I am not sure if that holds true if they use the "guest" access that is on some routers. When your friends log on, they will get an IP address from the router (providing you left the settings stock, it will act as a DHCP server and give everyone that logs onto the wifi their own IP address). You just need to use the addresses it gives you in the in game setup parts.
There are some settings in most routers that keep the wired side from seeing the wireless side (this is usually ON by default. There are other settings that keep each wifi computer from seeing the other computers on wifi, those are usually off by default, so you can all see.
if you need more info, please post the model of your router and also is it stock or modified software. I guess stock because of your question.
Have fun gaming !