it's not all hopeless. i've been in almost the same situation and i'm sure there's a few others around that have too. you never know, the situation may resolve itself as well.
i'm 19 now. my parents have just separated and are getting divorced. whilst the argument was going on it seemed like this outcome was negative. in many ways it is, BUT it actually turned out to be a good thing too in equal measure. it needed to happen. now it's all final it's sad, but actually everyone is a lot healthier and better moods, etc (mum's lost 2 stone, dad's drinking MUCH less... general household tension is wayyyyyyyyyyyyyyyyyyyyyy down) there's positive sides to divorce, foresight doesn't often pick them up. as i've said your situation may resolve itself again though.
also if they work so hard then they should have some sort of pension sorted out. it's not your job to have to care for them like that at 19! it could happen but it's more than likely you'd follow a similar path to them if you do go down that route. don't overstress yourself just because they're overstressing themselves. take time out and do what you want every now and then. you can help in other ways (housework, etc) and let your brother and parents worry about the money. feels like neglect, but in taking time out now you'll be able to help out so much more later when you're in a well paid job that you like.