Gear

Short answer is no.

 They are GTX, if you put the likes of wax on them, they won't breathe. Until they start to leak from the outside, no treatment is required.

 When they do leak from outside, use Grangers Footwear Proofer, Nikwax Tx. Direct Spray On.

What about wearing them around the house first before deciding to keep

Yes to that.

 Most shops will let you try boots/shoes, for a set amount of time before you have to pay for them.

 Good ones will let you take them back, try bigger size, change to different boot/ make, (with in reason), to find what's best for you.

 As long as you don't wear outside, or make any other changes to 'stock' boot. 

It's a wee bit too early to be drawing that conclusion. Apart from anything else those heatholder socks are thick and soft, not just thick.

Better maybe let him take them for a walk outside and experiment with different socks before you write off his purchase, eh?

"Sad to say Kevin, but if you need to wear super thick socks with them then you definately bought them too big".  Well, I suffer from cold feet and wear three pairs of socks sometimes, in my SLs and Mantas, these being thick, medium and a liner sock.  So it may be that the boots suits KM ok, if he needs thicker socks too.  Of course, the boots are likely to free up, giving more room - it'll be interesting to hear how he gets on. 

Hope they work out well for you, Kevin.