You say your twins had the same path growing up, but are you sure? It seems that one was intent on getting accepted to a prestigious school and plotting a career in business, and the other was devoted to art. B (the business kid) has a well-paying summer job lined up, and A (the art kid) will be going to camp to learn or teach art. These paths must have started earlier in their lives - they just didn't turn 18 and develop these traits in a poof of smoke in an instant.
Both career paths are admirable. We need business leaders. But we need artists, and medical professionals, and singers, and accountants, and kindergarten teachers, and researchers. The world needs the quiet dedicated scientists who spend their days and nights in labs trying to cure diseases, and it needs the performers who love dancing in the streets. We need garbage collectors and cable tv installers and cowboys and bakers and Marines.
Your twins may never be financially equal, but really, is that a good goal to have? Financial stability, sure, enough to provide for housing and food. Financial accountability and trustworthiness. Those are good goals. But equality, when one twin is business oriented and the other is artistic?
You might rethink your hopes and dreams for your kids. B might flourish and thrive in the fast pace of Wall Street. A might find true happiness teaching art. One of the most memorable people I met during my daughter's many hospitalizations was an artist who came to the ward to do art projects with the kids in the hospital. She had a tote bag of paper and coloring books and clay and pencils and crayons. It was such a joy when she smiled at a little kid hooked up to all kinds of machines who managed to scribble some colors on a paper. And the smile on that kid's face, oh, that was magic. No needles, no pain for just a few minutes. Just colors and creativity and an art teacher who accomplished so much healing with a tote bag of simple art supplies.
I can think of no better thing than to teach and inspire creativity. When you say that the best hope for A is to be a "teacher or something", I think you mean it in a defeated way, but I look at it as a potentially wonderful gift to the world. The best hope for A is to teach. That's awesome.
Of course A will have to work hard. Is it your goal for your twins to not have to work hard, to have money flow in like from a faucet? That's awful.
From your description, B sounds quite miserable. He sounds mean.
Help A understand that you love his creativity and his plan to teach art, and help him stand up to B. A doesn't need to be manipulated. Encourage his art and stop looking at money and income and prestige as the goals your kids should have. They should be honest, polite, encouraging, respectful, inspiring young men, regardless of their chosen professional paths. There are your goals. Now help your kids get straightened out. B needs kindness, A needs respect.