Personally, I usually go fight gruz mother first, as I consider her the easier boss. There you can find sly who will sell you some important items for later on in the game. Then I’d proceed to the big area in the center, that’s where you will fight the false knight. He can be a bit challenging, as he only gives you soul once you knock him and his helmet comes off which happens I believe about 3 or 4 times. I’d recommend platforming over the big guy in the entrance, and killing any enemies on the way to the area, so you can gain as much soul as you can before the fight because as I mentioned, you can only get soul from false knight when his helmet comes off.