I visited one of my wife's aunts for a while today. She needed a hand with a computer problem and changing a light bulb in her flat.
While I was sorting out her computer problem for her, I told her outright that I am a crossdresser. Not only was she not the slightest bit surprised, but she confirmed my suspicion that most if not all of my wife's relatives know but are choosing to pretend not to know. I believe that the term used in the military is plausible deniability. By not admitting that they know, it remains plausible that they don't know.
That's actually a big relief to me. They know and pretend not to, and that's their choice. The really good thing is that they continue to accept me in my male role. I haven't been rejected outright. I'm still trying to get my head around the larger implications of this, but it's definitely a relief.