A totally untested idea - as the game tends to be too easy anyway, maybe have a main hero with class sheet and for the other (three) characters don't use a class sheet at all and ignore XP for these - kind of like having NPCs.
This should make the game only slightly tougher (you still get equipment for the NPCs) and reduce the bookkeeping a lot. You could also house rule that the NPCs cannot be resurrected, you just play with one NPC less when they die.
I am using this when playing with my kids, the younger one does not grasp the complexity of the class sheets but can play along fine without it.
I really like this idea.