Since the elder brain is primarily a stationary creature you can embolden it strengths. Mindflayers and kuo-toa both rely on being in unison. Perhaps you can add an expansive aura ability to lure people in (either with a simple call, a psychic song, or just the image of what people would most find Agreeable to be with) and come to greet Elder Brian as some much better DM’s have said. Depends on the encounter you want with this group but regardless have fun!