I like the idea of their powers being identical to his but with light. I like the idea of their powers being able to create the pocket world when they get strong enough, that way they have to work harder to make it. 

Well I think it would make sense for him to be able to control a little light and vice versa because it would be impossible to have light without darkness and vice versa. So I would say he could control just enough light to make darkness.

Maybe their wrists would work but it would be a bit harder for them to hide.