Connected Devices on Network

Ok, so my home's WiFi keeps going out ever since we got rid of charter cable. My mom thinks someone might be on our network and asked me to see if I can find a way to see all the connected devices to our router....

The problem is that: I can see the client list (connected devices) via the router's homepage (type Ip in the address bar), but I can only see 3 out of 6 connected devices that I know of. My router is a Belkin Router and I'm wondering how in the world can I see the rest?