|You can also share the isp without recourse to wifi - or additional wiring; i.e. using the LAN over mains system.|
I tend to discourage wifi these days - unless it's absolutely vital to use it. This on possible health grounds (much discussed in places various); the risk of security breaches; the sometimes unreliable/unstable aspects of it all. Instead I favour the LAN over mains wiring system - e.g. Develo.
This approach uses plug-in modules - they go into mains-outlets; one for each PC and one for the router. The house/office mains-wiring carries the lan around the house/office; thus no need of other wiring, nor wifi...
Have been using the Devolo system for over a year; wouldn't go off it and can recommend the method highly.
There are other similar kits too; Netgear to name but one... However Devolo have regularly received the best reviews etc.; and their tech support has been OK on the two occasions I had a query to raise with them. The problem(s) I had were not Devolo related at all as it turned out (there was an oddity in part of the mains-wiring in one location); but nonetheless they were very helpful.
Minimum to aim for is the 85Meg system (roughly equivalent to 10Base-T); although there is now a 200Meg version as well.
More details on Devolo at:
In your situation you would need three modules (I buy them in pairs - usually a little cheaper that way overall); one for each PC - and a cat-5 cable to connect the module to the NIC in each PC; plus one for the router - and a cat-5 cable to connect the router to it.
Takes not many minutes to set it all up and then you're away... Want to move/change location of the router or a PC? Simply move the module to another convenient power-outlet. "Any" outlet will do - including "out doors" too be it a "permanent" outlet or via an extension lead.
Want to network a printer too? The same modules allow that via a suitable print-server adapter (Netgear/SMC/D-link etc.) which effectively mimics a PC...