T. -
Whew girl! You have your hands full! I have two kids that fight 90% of the time too! Such a treat to be confined in small spaces with them sometimes! :) But, things have improved on that with a few very workable strategies. One thing that works very well is love & logic parenting methods. I cannot stress that enough! It has worked wonders with my son and I wish I had known the strategies when my daughter was little. But, they work on all ages! You really should try them out. You can buy books or videos online but I usually just check them out at the library or the church's library. You could even probably borrow them from the counselor at your children's school...they use the methods there too! Also, we have two things we do at our house that has helped with the bickering: #1 Unless there would be hitting or something physical we tell the kids we WILL NOT listen. The majority of the time kiddos fight with one another is for "audience appreciation". If there is no audience, then at least with our experiences, the fight either doesn't last OR on the plus side - they end up working it out themselves which is obviously what you would want to happen. #2 If they do not work it out themselves then they both have to sit on the couch with no tv, nothing to do (usually holding hands,lol) until they are calm and agree to work it out. They HATE this tactic so they always work it out immediately - this has never failed! But ideally, you want them to just know that they are big kids and must work problems out with the person they are upset with. Rarely should you be forced to mediate.
I think if you try love and logic you would see some benefit. And of course be firm and consistent that you will not listen to constant bickering and they will get it and be forced to work through the petty stuff themselves making it much easier on you!
BEST OF LUCK! Hope you get some relief! :)