My dad always taught me if you couldn't screw 'em there would be a bounty on 'em. I'm not sure whether he was speaking of women or in-laws.
Don't blame me. My dad is a dirty bastard!
Not sure what your relationship is like with your in-laws, but I'd likely be having a chat that included the ramifications of telling others, etc. It doesn't seem as if they are morally opposed by their reaction. However, they (the uncle) need to understand that although this information is juicy and interesting; if it is shared with others it could result their niece and you being in a world of shit. I'd need whoever knew to look me in the eye and tell me they the understood the seriousness, and would take appropriate actions (ie shutting the F- up). If you are not confident in your in-laws ability to do this, I would likely either a.) finish up if I don't have much time left b.) shut it down / harvest early. No way I'd put my freedom in the control of someone elses ability to be discreet.