Try being happier and more positive yourself. Sometimes we get stuck in negative feedback loops with our kids. Don't let them push your buttons, and look for opportunities to have small special moments with each of them. Tell them every time you catch them being good.
I read a lot of parenting books when my kids were small, because they were quite a handful. One that really stuck with me described a mother who made a habit of caressing her kids or saying something nice, just "randomly". But it wasn't random. She was doing it whenever she saw them playing nicely or being quiet, or minding their own business. Since her kids were getting positive feedback when they were good, they would try harder to be good. I tried to be like her.
The other thing I found helped was consistently sending my children to their rooms whenever they were being obnoxious. I did this more with my son, since he was always grumpier and mouthier than my daughter. If he got annoying, I'd point to his room and say, "You can come back when you're ready to be civilized." When he came back, I'd just act like everything was fine and forgotten. Unless he'd done something really horrible, I didn't discuss it or make him apologize.
It eventually got to the point where he'd run off to his room the moment he started getting upset.
Raised voices were not allowed inside. I got right in there the moment anyone started yelling, even in "fun". I also can't hear disrespectful speech or whining. Funny how it works... my ears just seem to turn right off.

Sometimes I'd look up at the ceiling and say, "Is there a mosquito in this room? Something's whining. It must be a mosquito!" :lol:
I tried to get my kids to help me whenever possible. Even when they were very small, I gave them little jobs so we could all work together. When mine were your oldest's age, they thought it was a privilege to help me do dishes. I always told them how much I appreciated the assistance, and how nice it was to have big responsible people like them around to help me.
And hugs! Hugs are always good. If you want to kill the kid, it's probably a good time to give them a hug. Then put a movie in. Sit on the couch together and have takeaway for dinner. Let all the little stuff go.