In order for one person to buy life insurance on another person, the insurance company requires that an "Insurable Interest" exist between the two parties to the insurance contract.
Insurable Interest means that you rely on the other person for financial support, or that the other person's death would cause you economic loss.
Insurable Interest may exist between spouses, parents and their children, siblings, relatives, and business partners, among others.
In addition, you may need your brother's permission, and signature on the application for life insurance. He may also have to answer some health questions.
However, it is common for one relative to insure the life of another relative, so it is possible for you to get life insurance on your brother.
Learn more about how to buy life insurance on someone else.