My Grandson is being abused by his Father. My daughter does nothing to intervene. What can we do to protect him?

Our son-in-law verbally, physically and psychologically abuses our 8 year old Grandson. He is an angry man who yells at his son from the moment he awakes in the morning until he goes to sleep at night. He smacks his head, and we've asked him to stop but he is still abusive. He is small for his age, doesn't get fed properly (they go out to eat but order him nothing, saying he is not hungry). He wets the bed, grinds his teeth in his sleep and has developed a tick that throws his head back and pops his neck, even when he sleeps. My daughter does not protect her only child. I know she loves him. He is a bright young man, but they are turning him into a social time bomb. Our family can care for him, but we live 3 hours away by air and only get to see him once a year. What can we do?