Wikipedia has the correct numbers from Detlef Garbe the leading expert on this topic. There were 20,000 JWs in Nazi Germany, 10,000 were imprisoned, 2000 of them in concentration camps, and around 1200 died in custody including 250 who were executed.
This is the book to read on the topic.
https://www.amazon.co.uk/Between-Resistance-Martyrdom-Jehovahs-Witnesses/dp/0299207943
JWs opposed Nazism before the Nazis even took power.