There are intruders on my network

I have a router that provides both wired and wireless network. The input cable is Ethernet and there are a total of three people in my house, who use the internet. Two of us use cables and one uses a wireless connection. I also use a wireless connection on my tablet. I have installed a genie software on my computer that informs me whenever another connection is made on the network. Now the software is showing 6 people connected yet it is supposed to be 4 devices. Has someone intruded my network? How do I block them off? Can I find out who that is?
