Actually, only Porvus has been mentioned by mages in relation to the power. They thought it was Urvan at the inn because he was the only one they knew then. Again, these guys don't share. Being the only one with the power would make one irreplaceable and when your compatriots are as nasty as these, you need insurance. If Urvan had it at the castle, he could have easily taken over the whole kingdom.
I think it's assuming a great deal they can all do the mind trick. We know for sure Porvus can, but if Urvan had it, why didn't he use it on Sedwick rather than the shrinking spell or on them during the fight at the castle? As we've seen, the evil mages are greedy, jealous, and share very little.
This chapter highlight s the power and benefit of charms. The luck charm is working well. Their magic is increasing at each point before it is needed.
The battle with Skoda shows the wisdom of proceeding slowly.
If Lodda is as powerful as claimed, he will be fearsome and they aren't ready.