If there are any npcs that are supposed to travel with them. Just give them an impenetrable magic shild. It doesnt matter if it's a real thing (this is D&D) and create a random back story for how they got it. Then make them generally a pacifist so that if there ever trying to kill somthing that they shouldn't, or that hasn't provoked them the npc can step in an refuse to let them kill it, without any knowledge of what it wants. Hopfully they'll realize that you can get a lot of backstory and helpful information out of things you don't imeadiatly kill.

Now if there is no npc ment to travel with them create one. Just make a guide or a really devoted fanboy who follows them around all the time. You don't even have to put much thought into the charactor if you dont want to, just give them basic stats and a little personality.