So, I remember reading a book series in fifth or sixth grade, and I'd love to give my nephew a copy. It was about a young boy and girl who traveled between two worlds. One world had a magical veil blocking out the sun, the other was more of a magical spirit world. They could create hard light using stones that harvested sunlight above the veil. They also had replaced their shadows with sentient cloud-beings.
I remember the girl was rather antagonistic, and not very fond of the boy, she was from more of a viking culture, and he was from more of a magician culture.
I can't for the life of me remember it unfortunately, and googling is turning up nothing.