I recently moved my build along with the NPC's contained inside to a new cell using a cut and paste. But now the NPC's can not hit each other with their weapons, bullets just pass on through. I'm not sure if it's the cell itself that's the cause or the cut and paste I did. I've tried a lot of things, does anyone know what might be the cause?

I duplicated the "testjuan*" cell for the new space.

That could very well be why. That was used by the developers to test various things out when they first made the game, so who knows what effects it may have. You're best off using something that already exists in the game.