You made me care about the battle brothers and their thoughts, that's no small feat. Really engaging writing going on here.
Their GW counterparts are a lot more interesting in the novels, in no small part owed to the fact that they have plot armour glossing over their potentially higher casualty rate on the tabletop (at least back in 5th and 6th edition and prior).
Quite frankly I find your take on the Brothers more interesting than any 40K material I've ever read.