Honestly, in love with your Brook AU, I love how Brook and The Pack are just a whole ass found family (as they should be). I do wonder where Rex/Black Rook and Caesar/White Rook fit into all of this 👀
Thank you!! Black Rook/Rex and White Bishop/Caesar sadly don't mess too well with the found family of The Pack. It isn't because they wouldn't fit well it's just they're more off trying to prove something to actually focus much on what's going on with Brook. White Bishop is trying desperately to continue the nanite project and is fairly distant unless it's to reign in Brook and her antics where Gatlocke and Dr. Van Kleiss failed too. He's more like a boss, however more distant but also more destructive in his experimentation/inventions than White Knight ever was with Rex.
Rex/Black Rook is closer to Brook however his goal is the opposite of White Bishop, he wants to end the nanite project and all nanite activity in the most effective way possible. He acts much closer to Brook does, fitting in more of a mentor than boss figure but the line between the two can be hard to tell. Black Rook is trying his hardest to fix things and that means he can't spend too much time overseeing it's top assets: Brook. There is however tension between The Pack and Black Rook in regards of how she's treated and used for Providence and it's difficult for Brook. Because on one hand she does agree with Black Rook and his goals but not his methods but she trusts The Pack because they are like a family to her much like Gatlocke and Dr. Van Kleiss are, but they're more in line with the old goals of Providence. She struggles a lot with who to completely trust because it's a game of morals/goals vs family. However! Black Rook does prove that he does very much care for Brook by attempting to protect her when Providence is later under attack by a counter group (it's Six, Winters/White Knight, and Holiday and people who have joined with them.) He will put his life on the line for her, partly because she's the only way to succeed in his overall goal, but also because he has grown attached to her and has very much become a mentor figure to her over the time he's been the face of Providence.
So basically, White Bishop doesn't mesh well with The Pack. Black Rook doesn't mesh well with The Pack either but does with Brook one on one and becomes the mentor figure to her, a role which was not filled by anyone in The Pack (Dr. Van Kleiss and Gatlocke kinda fit in the weird and wild but also distant uncle kind of vibe if you will.)