I am unfamiliar with the movie, but I can see from the poster that Christopher Plummer and John Gielgud are in it. Both played Holmes.
That's two, there is at least one more.
I imagine the other connection is the crowning achievement of a stellar career, Malcolm McDowell in "Tom and Jerry Meet Sherlock Holmes".
Wow, I missed that one, and will add it with credit to you.Thanks.