You should definitely try not to push him as this might even discourage him. I remember before year 12 I didn't do anything but then all of a sudden I was serious about my education and was really motivated to do well. I'm sure when the time comes, your brother will start working hard because he wants to 
Yeah I really agree with this. Try not to work him too hard too early on.
I remember I only started trying in school when I hit Year 11 and before that I just played video games all day. I completely missed the selective school entry test (didn't try it) because I didn't care about school. But looking back I think it was all okay because I peaked in effort at the right time.
I've been overseas for the last three weeks so I've been having a good break. Though, once I come back I will still need to figure out what to do for the rest of the 6 weeks before uni starts. I'm thinking tutoring might be fun. Also, offers are coming up soon! Hopefully it all goes well for you guys.