my top tips, if they help.
Make punishments fit the crime. The are just kids, so rather send them to their rooms for 5 minutes ....10 x a day, rather than send them to their room for half an hour.
No TV for the morning, rather than the day.
ditto no games console...
Make sure you only warn once. But before you implement this rule, make sure you tell them that there's a new sheriff in town.
You could ask, in a calm moment, what THEY think he punishment should be for eg throwing the laptop. Their punishments will be far harsher than yours.
One punishment per incident. Its very easy to pile punishments on punishments for non compliance. There are exceptions, like destruction of property, when an additional sanction should be imposed. But only after the original punishment has been completed. Otherwise the behaviour escalates.
Plenty of exercise and plenty of good food.
Be consistent between you and your other half.
Don't get into an argument about punishments. They love this one....you end up screaming at them because they wont follow rules, rather than for the thing they did in the first place - its a big old distraction technique. Instead, for the one that wont go willingly to the room, tell him/her that eg you will not go to the park until they have gone to their room.
Plan an outside treat everyday for 2/3oclock or so - the park, swimming, snowman building competition, sledging, even a walk to the shop to buy an icecream or a bun from the baker. (you getting out the house will be of benefit too). They should know what it is, and look forward to it. Then you have a big ol' carrot for good behaviour. However, make sure they know what behaviours are expected.
For the screamer, when you tell her to go to her room, tell her the 5 minutes starts when she stops screaming. Tell her this before she goes upstairs....ie "Im sending you to your room for 5 minutes. there will be no screaming. If you scream, I will start the 5 minutes over again. You will spend 5 minutes in your room QUIETLY. Then you can come downstairs again. ou will not come down until you have spent 5 quiet minutes. That cantake 5 minutes, or it can take all day with you screaming. It is your choice."
For your destroyer, make sure he knows that for anything he breaks, you will take away one toy, on Christmas morning. He will have to earn it back with a week/3 days of good behaviour. And follow through. looking at a brightly coloured pressie under the tree for even an afternoon will focus his mind.
AFter Christmas, destruction of property should mean him giving up one of his nice things to pay for the thing he broke. Make sure he understands this in a quiet moment.
Then, before the throws something (i'm guessing he does it with an audience) remind him...."if you throw that laptop and it breaks, I will sell your ds and your Wii/your bike/your TV to pay for a new one. the smart thing to do would be to put down the laptop, or you will lose your stuff".
finally, I found this book very helpful.