as for brothers... my own impression - based on their solo writings - is that they both were quite clever, but Arkady was far much softer and less hopeless conflict generating author (and maybe person too), more emotional, while Boris (who is still alive) was much more "desperate" towards the human nature, less forgiving and more logical and "cold" compared to his elder brother.

Therefore I feel like Tarkovsky should be closer to Boris than to Arkady...