DH and I have 3 children between us, a son each from previous relationships and a DD together. Boys are 13 and 14, DD is 8. We all live together, SS moved in with us over a year ago after having problems with his mum and step dad. My DS and DD get on well, whereas SS and DD argue constantly. They say things to wind each other up, they snipe at one another all the time. It's really getting me down and I don't know how to make it stop. We've tried talking to them, together and separately. It's so bad I can't even leave them alone in a room together without worrying that there'll be a row. I am so stressed by it all.