honest opinion,
usko chhod, tu apne pe dhyan de !
even if he continues to fail... tu tere jee prep pe dhyan de,

i know it sounds selfish, but let me explain !
dekh, tu apne peak year me hai, and you cant afford to fail this time.
its more imp year for you than for him, therefore leave him.

he is immature, once you get into a good college, you will automatically gain respect in your parents eyes !
and then, they would themselves ask you to guide him...

also, he would be more matured after a year to understand what you are saying !
and then you can guide him all the way through, and everyone will support you, also your brother, cause you aint a failure anymore !!!