Networks Case

I recommend to the family to set up a WLAN. The reason is that is much easier to connect the devices via wireless than with a regular LAN cable.
To make the WLAN I suggest for them to buy a router (approximately $ 150). A router is a network hardware that is used to connect together two or more networks. A typical router will use a cable plugged into it to access the Internet and will have more cables to set up a LAN. In this specific case, I recommend only one cable connected to the desktop, while all other devices are connected wireless.
For the extra software to the network, I recommend an extra firewall between the LAN and the Internet for extra protection. The price of the router already includes the fire wall. Apart from the firewall, I believe that the family may want a filter. There are many filters on the market, I investigated one called Net Nanny (approximately $ 40 for one year license) that provided everything the family may want to block, from pornography to some social networks.

The network will be like the diagram shown below. As you can see, the topology used for this network is a star topology. If one of the components between the client (device) and the router gets affected, the other connections are not affected.