Usually, there does exist some insurable interest between spouses, siblings, parents and their children, as well as, business partners.
You also need your brother's permission if you want to be the owner of a life insurance policy on your brother.
Your brother may need to sign the application for life insurance, answer some health questions, and perhaps take a medical exam.
Does he work with you? Does he owe you money? Are you dependent upon him in any financial manner? If not, what would your insurable interest be in your brother?
Here's an article that explains how to buy burial insurance on someone else.