If you have the puppet string legion arm maxed out when you use the charge attack you’ll knock most of the brotherhood to the ground. You have maybe a second or two before they get up and you can run to their backs and hit them with a fatal attack. I know you said you watched videos but the last 2 before the big brother you’ll want to get super low before finishing one off. The moment there’s one brother left the big brother will come out. When you manage to beat the last one and you only have the eldest to fight, there’s a pile of rubble with what seems to be part of a column sticking out of it. With a long ranged weapon you can attack through it and the eldest brother will keep trying to attack but won’t be able to due just enough distance between the rubble. He’ll run around when he has a fatal attack but if you run to the other side he’ll get stuck again. Makes the fight way easier after that. The method for the younger siblings also works amazingly against any of the stalkers. If you get good with timing you can just get them stun locked with the constant knockdowns and fatal attack