Word to the wise: if your teenagers announce that they plan to flee the coop as soon as they are legally able to do so, and especially if the announcement is delivered belligerently, you need to beat them more. A lot more. If you beat them severely enough to get Child Protective Services to remove them from your custody, all the better. Otherwise, mark my words, you will wake up one day with a 25 and a 29 year old living in your basement with their assorted partners and their progeny, they will spend their leisure time trying to rip each others' throats out, and you will spend your golden years hiding in your room and chomping down anti-depressants like so many Pez candies. I know whereof I speak.
To be fair, sibling rivalry was a part of my youth too. But it disappeared when we established our own households, and my brother is now one of my favorite people in the entire world. He too agrees that beating teenagers more is an excellent deterrent to their setting up permanent residence and thus effing up one's retirement.
Let's face it, adult siblings were never meant to live under the same roof, especially if the mortgage to said roof is held by their parents. The argument that our forefathers in the pre-industrial years lived that way does not hold water. They died at forty, not because of lack of medical care, but because they wanted to.
Beat them. Or it will come to the point where the only way you can get rid of them is by calling the police someday after the nine hundredth Olympic grade screw-up and/or subatomic explosion, and having an eviction notice witnessed by the heat. I'll get back to you as to whether that worked or not.