So Grey Knights, they are 8 brotherhoods with the Purifier and Paladin orders staying on Titan to guard shit. But the two kits for the Grey knights are named after and are these two orders even they its the other 8 that do the fighting? And the Paladins and Purifiers don't leave Titan, like the old custodes lore of never leaving the Palace. Why did GW make this decision/ how does this work? Am I being dumb and missing something?