Yes, I learned that lesson the hard way. Be dignified. Never let them see you sweat. You aren't their buddy/peer, you are their father's wife and their elder. Insist on being respected. Act too eager to get along with them or to please them and they will take it as weakness and they will eat you alive. Keep detached from the get go. 18 years old is a grown up as far as I'm concerned. Let him show you how he wants to be treated. If he's pleasant, be pleasant. If he's a jerk, let him & DH know loud and clear that you won't tolerate this treatment and stick to it. Or if he's better looking and has no baggage, maybe he's more your type (just kidding)? Good luck!