Here are pre-existing into posts of mine about my two favorite Holmesian tie-in canons:
Miss Madelyn Mack, the one where they're lesbians in pre-WWI New York City: Meet Miss Madelyn Mack
Their Majesties' Bucketeers, the one where they're aliens who do everything in threes and the Watson figure is a surmale and rhe marries Holmes and Irene at the end: Mymy/Mav/Vyssu, OT3 4eva (post also includes reviews of books in the Irene Adler series and the Mrs. Hudson mysteries.)
The ones I talked about a lot
Miss Madelyn Mack, the one where they're lesbians in pre-WWI New York City: Meet Miss Madelyn Mack
Their Majesties' Bucketeers, the one where they're aliens who do everything in threes and the Watson figure is a surmale and rhe marries Holmes and Irene at the end: Mymy/Mav/Vyssu, OT3 4eva (post also includes reviews of books in the Irene Adler series and the Mrs. Hudson mysteries.)