Casting is the same, you can use a base class to do iperations, such you can have all your npc character classes extend a class called base npc with the functions on it that are common to all.
You describe what you are trying to cast to, but you dint say what you are trying to cast, it actually has to be the object you want for it to succeed. So in the level a trigger will activate on a character probably, you can cast that actor to your base npc character class. Or on a projectile hit in the projectile graph cast the hit actor to the npc base class etc.