I am so sorry you have been through so much grief and now again you have lost your brother, your support.
What you are feeling is real, and it is so difficult when we find ourselves so alone in our feelings, when we cannot make ourselves uinderstood, people just do not know.
One thing you must remember, the accident was not your fault, your parents cannot blame you, I think they are hurting and trying to find blame as an explanation of why it happens, deep down they know you are not guilty.
The road to recovery is just one step at a time, sometimes we think we have managed a step forwards to realise that we are back to the beginning, eventually it becomes easier to deal with our grief, we never forget however we accomodate our grief into our life, at times we will cry, but it become easier.
Try not to ask yourself too many "why" or "if" I have learned that these questions never have an answer and can destroy us even more, you have a right to be angry, to cry, to scream, it is part of grieving, it is hard not to understand why these things happen, why all of a sudden our lives are touched by grief, we feel so hopeless, so sad, so mad, all we have is hope, hope that somehow we will be able to keep going, to rebuild our lives.
I will keep you in my thoughts