how many do you think never get caught doing a "gross sin "? And how many do you think actually get caught? How many people confess? How many do you guys think practice gross sin and not get caught?
I find it hard to be accurate since many of us were JWs for a longer time than others, also because some of us were nosier than others, and also because some of us were in different congregations and therefore knew (of) more people.
I'm also basing my answer in the presumption that you are using the WT's definition of a "gross sin", which includes my very own existence.
As a gay JW, and growing in a culture and medium that wasn't too kind to LGBTQ+ people socially, legally or any other way-ly, I got to know quite a few JWs with a double life. Never counted how many, but through my entire life in that organization there were many people in the congregation who had double lives.
Me personally, I can fill the entire quota of "gross sins" based on their definitions of things that they believe people should get killed for, regardless of how decent and morally clean they are. Their criteria for sin is ridiculously, insanely, stupidly narrow and specific, so pretty much every single person at some point will do something that is considered a "gross sin".
Getting caught in the sense of people knowing, a lot. Getting caught in the sense of anyone in the congregation taking any actions, very few. I think those two last statements also answer your last question.