High gaming ping when multiple users on same router

Hi, I live in an apartment and there are three of us. This is what devices we have:

Wireless-N Broadband Router WRT160Nv2, and three wireless adapters that work fine.(two rosewells and a trendnet)
Two computers are custom built PCs(1year old)(built with tomshardware's help thx btw) and one HP laptop(one year old)

the situation:
when surfin net we are all fine and experience usual hiccups. when the two custom PCs play the same game with different cd keys we are fine with pings of 50 on the servers we like to play on. Any game actually is fine on these computers when online.

the issue:
as soon as the laptop joins online gaming or even high internet usage the two PCs get high pings upwards of 300-350(unplayable)
on one game hes using the same cd key as another(if relevant idk) and the computer hes using the cd key from, has the ports forwarded to its static ip.

our hypothesis:
1.) router needs a specific settign adjusted
2.) laptop computer is source of issue
3.) isp provider
4.) port forwarding
5.) cd key used on two comps

Any comments, suggestions are welcomed. thanks you guys are the best.