Wireless Connection Issues When Connecting a 2nd Macbook?

I am new to Mac. I recieved a Macbook about a month ago and have one working Windows PC conected to my wireless router. I also have 2 iphones and 2 ipads that connect as well. My bf bought a macbook and just recieved it earlier this week. We set up and connected to the internet no problem. After 10 min of being on the internet together the internet stopped working on both macs and the windows PC. I have to reset my router and modem...then internet works again for 10 min. Repeat....Sometimes i get a error message on macbook saying another device is using the same IP address.I tried going into network preferences Advance and tried renewing my DHCP Lease option on both macs. I tried calling my ISP and tested the modem with other things and it is not the ISP. I tried to see if it was the router settings- which i changed to different channel frequencies and i reset the WEP to WPA-personal as i read that might be an issue with MACs.I am fine using all apples devices, 1 MAC and the PC with no internet issues. But as soon as I connect a 2nd Macbook- issue every 10 min.