I am just at the end of my tether with the kids, and i need to get it out... DH doesnt see what they are like as they are great (most of the time) for him...

MOst of my problems come down to Xander. He used to be an angel, then he hit about 18 months, and he changed. My 16yo brother taught him to swear (DH and i dont swear, ok we do, but only rarely, and NEVER around the kids.) We were told all kinds of different way to rid him of it. Ignore him, he wont get a rise and wont use it anymore. Naughty corner, all the usual kinds of punishments. Even the odd smack. nothing works. I had DHS around for a follow up visit, and all Xander did while they were here is ask for things. Coke mum, chocolate mum, and when i said no, he's start. "Fu*k you mum, my house, go away, dont love you fu*k off fu*k off." He just kept on and on. I ended up sticking hi in his room, i just couldnt deal with him. He picks on his younger bro (i know they all do) Declan's 19 months. Xander scratches him (he has a massive red welt across his face, with streaks of blood where he broke the skin) and Declan didnt do anything except be playing with a truck Xander decided he wanted. He smacks Anneliese, and holds his hands over her mouth and nose so she cant breathe. But he only does it when he thinks your not looking. He acts like the pefect loving big bro when there's people around. I've tried most methods of parenting with him, anything people have suggested i've tried. I've taken to either ignoring him and giving attention to the one's he's hurting, so he see what hurting people won't get him attention, or just ignoring him when he's yelling at me (but not hurting anyone) Im afraid ill just snap and i dont want to do that. Just then, him and declan were playing happily, and all of a sudden Xander pushed Declan over so he smacks his head on a tonka truck. No reason why, he just did it. I try cutting additives out of his diet, but it wasnt working. DH was slipping him lollies, coke, chocolate, macca's. Dh doesnt believe he needs the diet. I try and divide my time between 3 children and spend time with each one on one, but Xander is just taking up so much of my time. Now he's walking around telling everyone "You shut up fu*kin hell." thats one of his favourites. He's destructive, rebbelious and a rude little... i dont know. I love him, he's my son, but i really dont like him. I dont feel i've really bonded with Anneliese, all of my time is spent trying to protect the kids from Xander. Declan and Anneliese are fine, Declan plays quietly, try's to keep to himself, is loving and cute, Anneliese is a 4 month old, doesnt do alot... Anyone got suggestions? Im willing to try anything...