Responsibilities

My brother call me and told me my stepbitch should take Responsibilities of her son. He said its not my responsibilities it's not my kid. I told him I know but I am a adult and if his mom not around. I have to take care of him. He only a little kid. I told my brother he might have to help me if he could. If his mom does pull this stunt on me. He said he going to think about it. I hope he gives me a hand.