i'm Not an expert nor I'm famaliar with similar cases, But both reply above forgot to relaize that your brother is under 21. There is something different for under 21 and unmarried, but not through you.

the way I see is that you can apply for your parents and they can apply for your brother. This seems to be a faster route.
DOnt know if your parents have to wait until they become citizen or they can apply while they have greencard.

Also, I dont know if you can apply simultaneously as a derivative for your brother while applying for your parents since he is under 21 and still under the support of your parents.

No matter what- this is much faster and better than you applying. Not sure how old is your brother. But there is a provision in the process (not sure the name) that while filing if your brother is under 21 and later on if he turns 21 during the process, they are still considered under 21.

If I were you I would spend some $$$ on initial consutation with immigration layer; its worth spending 50-75 $s for 30 mins on your case.Thanks,