First thing I'd do, is look for any firmware updates for the router. Then double check the settings for the password on the wireless connection.
If it's WEP, change it to WPA or WPA immediately, if not sooner. WEP can be cracked in a matter of minutes, and someone could be stealing your bandwidth without you knowing. WPA is much more secure. Then you have to double check the settings on your sons' laptops. Make sure that they match the router's settings. And despite all the claims of "easy to use" this still requires at least some basic knowledge of networking.
You also left out the OS revision your sons are using on their laptops. Also whether or not they have been keeping up with updates to the OS. Is it 10.3, 10.4, 10.5, 10.6? And what number after that? Like I think 10.3 got to 10.3.9, 10.4 is 10.4.11, 10.5 is 10.5.8, and 10.6 just ticked over to 10.6.3 Monday.
Finally, if you get an actual ethernet cable and connect them directly to the laptop, does that work?
We have wireless in our home which works fine with our HP laptop everywhere in the house. Both college-aged sons have Mac laptops and often are unable to get wireless when at home (one gets it sometimes if he stays on the first floor, the other can't get it at all) What gives? I know nothing about this stuff but I do know our service is through Comcast and has been very reliable, and our router is probably fairly old.