Thank-you for your reply.
I've returned the ASUS router to the store and gotten another TP-Link WR841N. I haven't had time to hook it up yet.
The cameras are older than the ones you use, and only use 2.4Ghz. They are connected to the wifi through the DLink Lite app. Basically you scan the QR code, press the WPS button on the router, then press the WPS button on the back of the camera for 6 seconds. The camera is supposed to connect to the wifi.
Until my old router started acting up (slowing down internet, resetting itself, dropping devices) connecting the cameras to the app took only a few minutes each, and to the wifi, only a few seconds each.
I'm pretty confident that since I've gone back to a router developed around the same time as the cameras, that everything should connect easily again.