Was he actually fitted for these boots? If they were not fitted in a shop it would be worth taking them to a decent fitter and have the overall shell volume compared to his foot. If the shells dont work out, then changing liners and footbeds will do very little. So before putting more money into the boots go have someone asses his foot in them and see what needs doing.
If I had to guess I would say they are maybe a little big. If he could stand around for a few hours in them before they have been fitted, and they feel ok chances are they are a little big. Normally a snug boot will be pretty un-comfy to stand in before it beds in. I can normally manage about 10-15 mins before my feet are numb in new boots. The fact they hurt when he skis further confirms they may be a little big, Im guessing his foot has room to move inside and its because of this he is finding pain in the boots.
But Im just guessing so go get them looked at.