The PCs: 1 is 2013, the other c.2012 or perhaps 2011. Both Windows 7. They're certainly not used for any performance demanding applications, Word, Excel, web browsing, Outlook, and the odd photo organising program (similar to Picasa).
The wifi signal would have to go across 15ft or so of open space and through a stud partition wall to the bedroom they'll be using as a study. Although the study would have lots of shelves with numerous books on, I doubt signal strength would be an issue. However at £16 or so the Edimax Ew-7711n seems reasonable, providing there's the spare slots for it
I'm over at their present house Friday so will check.
We have more and more laws, and less and less enforcement