My 2 DDs (14 and 9) simply cannot get along. They are lovely girls when apart but rub each other up the wrong way. DD1 is v emotional and shouts and screams if DD2 winds her up or worse, which she does frequently. DD2 doesn't seem to understand the effect her behaviour towards DD1 has and enjoys the (negative) attention from her. Today DD1 came back from camp and within 2 mins they were shouting at each other and now they're not talking, because DD2 rearranged a few things in DD1's bedroom as a joke but DD1 did not see the funny side as she had to put it all back. I spoke to DD2 about not touching DD1's things but she didn't seem to care.
OH seems to think this is normal behaviour between siblings of these ages but I don't think all siblings are like this. Any advice gratefully received.