Is this guy a terrible person?

Elliot and Milo are 17 years old. Their sister, Sierra is 22. Unfortunately, Milo is the golden child and their parents make it obvious that Milo is their favorite because he makes the best grades and will most likely make the most money when he grows up. Elliot hates Milo because of this. Even considered stabbing him in his sleep he was so angry. One day Elliot decided to spy on Milo to catch him in some dirt so he can blackmail him into doing his exam for him.

Milo does everything Elliot says but that didn't stop Elliot from stealing his money, breaking his nose and threatening to kill him/ expose his secret if he told their parents what was going on