Your brother is lucky, indeed, to have such a caring sister. Unfortunately, you and your mother probably can’t convince him as long as you are in a fight with him. Although I absolutely agree with you that it would be better for him to finish high school, I know that fighting with a teen who is on a mission never goes well.
It might be more effective to talk with him about how he can get ready to leave. That means getting an after school job and saving enough money to be able to get that apartment. It means identifying and learning whatever skills he needs to successfully live on his own.
Does he know how to shop, make decent meals, do his own laundry and manage money? Does he have a realistic budget for what he will need to support himself? Does he have enough money in the bank to buy a used car when he is old enough? Does he know what he needs to do to maintain one?
Don’t overwhelm him. Do have a serious talk. Stress that you do want him to be successful out there but you are concerned. He won’t be at home for the important years when most young people make the transition to adult life. Sincerely offer to give him a crash course over the next months or year to help learn what he needs to know to be independent and successful. If he takes you up on it, do keep your end of the bargain. He needs to learn those skills for independence regardless of what he decides to do about school.
Meanwhile, encourage him to teach you as much as he can about the power of chi. See if you can come to an understanding of why it is so important to him. If you express interest, he may not need to be in such a fight. If you learn more, you may be able to have a more useful conversation with him about what he needs to do to pursue that interest and be taken seriously in the world.
You may not be able to get him to stay in school. That would be a shame because it is much harder to get a high school degree as an adult. But it can be done. The most important thing right now is to stay in relationship with him so that he has a home to come home to and his pride won’t get in the way when and if things fall apart when he tries to live on his own.
I wish you well.