Source: The Great Interpretation of Dreams (Ibn Sirin)
A laughing (smiling) brother in a dream indicates strength, support, and goodness coming from him.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
A laughing brother indicates joy and benefit.
Source: Signs in the Science of Expressions (Ibn Shaheen)
A laughing brother is interpreted as goodness and joy.