I don't know how to do this!!!!!!

Ok, so I have been having discipline issues with Hali lately. Things are pretty nice and quiet until I pick her up from school. Once she walks in the door or even on the ride home all S&*$ hits the fan. I don't know if she saves it all day for me or what but she starts in on Leiton. I don't even know what happens but before I know it hair is being pulled, punches are being taken and someone is seriously crying! Before I know who to punish they start again blaming and whining and then hitting and then I lose it. Once things calm down a little we start homework or they play games or just chill in their rooms. TOday however I had to take the trampoline down for the winter. I can' even say what happened...it just excilated to a point where Leiton was whipped on the ground and hit his head. I told Hali to go inside and I thought she did. No. I tell her again she says no. I count to 3, threaten to take items away and all of this goes on until I absolutely lose it with her. Our next door neighbors are outside by the way who we don't get along with and Leiton is crying. I scream at Hali (we are in the garage now) to get her butt inside. I chase her in and with her boots on full of mud she runs to her room and slams the door. I push my way in and she now has mud ALL over the carpets! I really thought I had lost my mind I was so mad at her. Now I haven't talked to her for over an hour and I am still mad. Yesterday she kicked a hole in Leiton's bedroom door because he pulled her hair. What is going on ???? I can't do this anymore. I need this to get better!! I am becoming wicked!!! Leiton of course is the first to come to me and hug me and say "I love you mommy and so does God". What a sweet boy. How can I get that out of my 7 year old daughter??? I need to find an older child Baby Book. I wonder if Dr. Sears has wrote one of those. I may have to check.........