DreamsMaster: Dreams have many layers of meaning, and I don’t rule out the possibility of spirits communicating to us through our dreams. Regardless if this message came directly from your dead friend or if this friend in the dream is symbolic, it’s quite possible that you intuitively sense your brother is in some type of risky situation, and the dream is sending you a message to take action to protect him.
On a symbolic level, your deceased friend could be a shadow figure, a part of you that may be somewhat hidden from yourself and that you’ve projected onto this friend. For example, in your waking world you may be reluctant to confront others, but this friend or shadow represents a side of you that has the courage and assertiveness to speak your mind. Think about how you would describe this friend, what personality traits you would ascribe to him or her. Then, consider how you identify with those traits personally, and this may help you understand why this particular friend has appeared in the dream. Warning your brother on behalf of this person could be a way of drawing courage of your own to approach him about a situation you perceive to be risky or threatening.
Your brother in the dream may be literal or symbolic as well. On a literal level, as mentioned previously you may be intuiting that your brother is indeed in a precarious situation that you feel the need to warn him about. If it doesn’t feel like it fits that your brother himself needs to be warned, then it’s possible your brother may be a symbolic representation of yourself or someone else in your life. Just as suggested you do with the friend, think about how you would describe your brother, and then consider where in your life you identify with him and may need to be cautious yourself.