I can totally, totally sympathise!
I have four dc, numbers 1 & 2 - a doddle.
Then came 3 & 4 - twins. One is now - just about - getting the behaviour thing. More often than not she won't argue the toss about absolutely everything, comes when told to etc etc. Not always, but is so much better than even 6 months ago (they are 5 and a bit and in reception).
The other one - well bloody hell, she drives me mad and I am that mother! Shouty and irritable and often feeling out of control of parenting!
However......... I have recently (and I mean only during the last two weeks) implemented a new plan. Now this child loves sweets. I know all kids do, but she is slightly obsessed with them. So, on Monday, I buy them both a packet of sweets - this week jellybeans. And then, every time they misbehave, argue back at me, have a silly strop, don't come when asked to etc etc - I EAT ONE!!!
Oh the power! God I love it!
Then on Saturday afternoon, they get to eat what's left.
And I must say, it seems to be working. I don't feel quite as shouty as before. I do not reward good behviour as such - tried that - failed dismally. Instead, I eat a jellybean when they misbehave!!
So, it's up to them how many sweets they get at the end of the week.
Try it and see...