Not that it likely matters now, but the brother sounds like a high-functioning schizophrenic - super-bright kid morphing into an increasingly erratic and aliena

Not that it likely matters now, but the brother sounds like a high-functioning schizophrenic - super-bright kid morphing into an increasingly erratic and alienated adult. Especially without any hallucinations, it's tough to diagnose and looks like a mix of depression, mania, OCD, etc. There's the flight-of-ideas component that frequently allows for great creativity, but frustration as the world can't keep up with their changing visions and priorities. They also tend to be narrative-builders - nothing just happens, everything has a cause, often malignant, byzantine, and vast. Because they always feel 'on' and 'deliberate' everything else must be functioning that way too, so everything is a personal attack. They increasingly can't work with others and try to work as brilliant loners or establish themselves as the visionary leader.