Re: Any tips would be welcome (even 2x4's)
It appears that you have lost control, not only of your temper (really easy to do under the circumstances) but also your children. They sense this and feed off of it. I was once where you are now. Two daughters 1.5 years apart. They never got along -- always vying for my attention (still do to this day). Hey it was rough. It seems the more you try and let it go, the worse it gets. And it just keeps building and building and building up. . . until there is an explosion; and then you end up hating youself even more then when it started.
One thing you can't do is reason with children this age.
Take a stand and hold to it. The oldest should lose something that she just can't live without -- Temporarily.
Ya know, I have been through this all before -- as mentioned earlier; however, I seriously don't remember how! It was hell there for a while. But. . . point being, you will and your children will survive this.
Best Advice: Don't let them get to you, no matter how hard all three of them try!!!!!