Clear set of rules ie no violent fighting, no swearing, no taking each other toys without asking first, making their own beds, helping clear up after dinner etc etc whatever your rules might be. Make them very clear, maybe write them down, put them up in the kitchen.
If they do not comply, they have to be punished.
If you just say, for example, no DS, but they are allowed to watch tv, then it is not a punishment. No ds, no computer, no tv, take away books, magazines whatever they might want to read/play with from their rooms. Send them to their bedrooms. No dessert etc. For as long as necessary. I bet if they will consistently get sent, separately, to their rooms, with nothing to do, for, say entire afternoon,they will think twice next time (it will take a few times for them to realise you mean business).
It isn't really that complicated, it's about making sure they know it's you and your dh who have the authority in the house. Shouting a lot, spanking etc won't do anything. If they behave in a way that's not acceptable in the family/society, they should be removed from it.
You need to assert yourself now. When they will be 15, it will be much, much harder.