I'm trying to sleep but my brother wants me to come help me with his homework even though he had all night to do it.
Did he ask you for help earlier in the evening?
No. This is the first time he asked for my help.
Although it's good to help family when they need it, it's also inconsiderate of him to expect you to lose sleep due to his own irresponsibility. Hopefully he will learn from this and gets his work done earlier in the future.
I doubt it, but let's hope.
I think if you explain to him tomorrow that you were willing to help him, but that it was rude to expect your help so late at night, he will understand. Just be polite about talking to him. I think he will take this as a good chance to learn why it's important to get work done early.