Parental Obligations

Q. I have a 17 year old half brother that my father has custody of. My father threw him out last year when he was 16. My dad does not support him. My half brother is sick and needs a spinal surgery so he called dad to tell him since he is in dad’s insurance. Dad does not want to have anything to do with my half brother. Isn’t he obligated to help since my brother is only 17?