Sex at each other's parents' houses?!

Ok so he's not my bf but he was and we still hang out and visit each other in the summer. (We're in college) we have sex when ever we see each other. I just feel uncomfortable having sex at each other's houses like I even though my parents know I have sex still it's like uncomfortable. Plus my sister is 13 too and she's home a lot. Like his family knows we have sex and my family knows like I'm so weirded by it.. Anyone feel the same way? When people are home, we're quiet..