Wow, that sucks. Okay, so your dad is moving to Perth, which I believe is in Australia. Okay, off topic. But, your dad is moving to the other side of the country, your family's income is getting lower, you and your brother fight, and your dad was $70,000.
First of all, your dad doesn't seem to take into consideration that if your mom can't pay the money, that you'll lose the house. Apparently, he doesn't get that HIS KIDS are living in that house. Maybe your mother could go to court to get alimony or spousal/child support (though I don't know much about the Austrailian legal system-sry.) I mean, couldn't she take him to court to get the house under a divorce settlement, or is all of that already settled. I know that you wanted to keep it short, but to be frankly honest, its not easy to give advice when I don't know much. I mean, have they already gone to some type of divorce court or anything? Now school......being in the divorce situation, it can make that very hard. Are you sure that you aren't developing ADD/ADHD. Does Australia have any kind of welfare/income-based system for medical coverage. I mean, you said that you guys are running low on cash. If there was something available in the form of state-paid medical coverage, then it could be possible to see a trained professional. Then they could diagnose a possbile attention-span issue, and maybe after several evaluations, the evidence from your case could lead to a triumph in court.
This is too long, I know. But, if none of this is possible, let me know, and I will try to help you think of a solution, because there is one, it's just hiding itself. But, we will find it, and things will get better
PM me if you need to talk.....I am always listening.