From: In my chair
"How do I bring up that they need to control themselves?"
You don't. You're just going to have to accept that your parents are sexual beings, and that sexuality is part of being an adult. When the time comes, you will probably be just as flirty and sexual when you are in a healthy relationship.
That said, if I don't miss my guess, it is probably normal for a teenager to start realizing that his/her parents are sexual beings and suffer a minor level of shock as a result. I remember being annoyed at being kept up by my parents having sex when I was a teenager - perhaps it was because I was finally old enough to be trying to get to sleep when they were likely to have sex in the first place.
All that said, if this still bothers you, and you still feel the need to speak up, remember this: you are in your parent's house, living under their rules. They do NOT answer to you. So any problem you might have with how flirty your parents are or how often they have sex at night is YOUR problem, not theirs.