So, I forgot the title of a book and I was wondering if you could help.

It's about a girl with a younger brother and they live somewhere and they have to gather scrap metal and sell it. One day, a storm or toxic cloud or something happens and the boy gets sick. He recovers and they make friends with a odd girl and when she is kidnapped, the siblings board a train to look for their friend. The people who run the train are supernaturals. The fire stoker can control fire and a young boy can shift into a mythological animal or something. She finds out that she can control machines when she accidentally explodes several guns. When the lost girl is located, it turns out that she is a robot of sorts. I can't remember the rest.
Thanks! :)
P. S Please give only relevent answers!