This is an interesting reader question! Because, as far as I know, my Black Dagger Brotherhood Reading Order list is pretty exact, and quite intensive (having preorders as far as into 2023). Even spinoffs, and novellas all in the right spots.
That said… now I’m super curious as to an answer for Cheryl’s question.
I was checking this series out on goodreads as I’ve read most of them.
Goodreads said there was a related series the black brotherhood. When I checked it out it was in german. So I’m thinking no big deal.