Once I've installed the network ability I'll connect them to my wireless router for testing. When I've done that they'll be ready to connect to the proper router when returned to the friend's new home.
If I also bring their router can I power it up, albeit not connected to my telephone line, and set the PCs up to connect to that wireless network. This will save a small task when I return them in a week or two. I can't see why the PCs should not be able to connect to the router but won't of course be able to get to the internet.
We have more and more laws, and less and less enforcement