I think that If I were your age and still in school I would try to stay and help others. I felt I had to leave rather abrutly since I had a child and did not want him exposed to it.
I think being calm and rational, formulating a long term exit plan and a path to help your brother would be in your best interest. It sounds to me that if you leap too soon the emoational upheavel my be too much.
I'm sure by now you have read many experinces on this message board. Many are bad, but some are good.
I think in partucular I read the reddit message board where there are lagre percentage of younger people, the common advice is to finish school, use the time to make outside friends and have a place to land when you leave.