I think there are a lot of different ways to write this. I would “show” not “tell.” It could work to write mainly about your brother with a last paragraph tying it to you. The way in which you write about your brother also shows a lot about you. I would avoid clumsy efforts to focus on yourself when you could write an effective essay mostly about your brother that would "show"about you without explicitly “telling” about yourself, but make sure to tie it in in the conclusion.