I am a little bit shocked by the fact that both you and your parents are blaming a 5yo boy for the difficulties in the family.
Most of what you tell us (apart from throwing stones at cars) seems totally normal for a high-spirited 5yo. It's the parents job to deal with it. He is not responsible for the fact that you were a different type of child.
Otoh your parents seem to be handling this really badly. Not letting him do anything fun at weekends because he misbehaved at school is going to be totally unproductive with such a young child: they have a short attention span and any punishment needs to be immediate. All their present approach is going to do is to strengthen him in the idea that he is a bad boy who doesn't deserve having fun so he might as well carry on being naughty.
As a previous poster said, your parents need parenting courses to deal with this.
Another possibility is that your brother's behaviour masks MH issues very similar to your own and that while they are coming out as depression in you, they come out as wild behaviour in him. That again would be completely normal. Very unfortunate as it's going to require your parents working double hard- but again, it wouldn't be his fault, any more than your depression is your fault.
It must be very hard to go through A-levels while suffering with depression; my own dd did that and I know what she went through. At the same time, we both also knew how tempting it was for her to blame external factors when she felt she wasn't coping. In her case, the things she blamed (boyfriend trouble etc) did no harm. You could do real harm here by letting a 5yo child think he is responsible for your illness. It could ruin his whole life.
What you need to do instead is this:
speak to your parents about the possibility of some course that would help them to deal with your db
when speaking to your parents and to yourself stop speaking as if your little brother was to blame for all the problems in your family- just think about how you phrase things
carry on with the support you are getting- and good luck to you; it's a tough and brave thing to do A-levels whilst struggling with depression 