On a family vacation with not just my immediate family, but my aunts, uncles and cousins to Key West we were all staying in this large rented home. Many of the bedrooms had windows that looked out onto the pool area and I had happened to go and take a little snooze after dinner in one of the lounge chairs. I woke up probably around 8ish or so and glanced into one of the windows to see two of my cousins having sex with each other. This kinda made the vacation a little strange as after that I started seeing them doing subtle little things that made it obvious to me that this had been the norm for a while. I don't think I will ever say anything about this though because I don't wan't to make family gatherings weird and it's not any of my business really.